System and software for matched aligned and unaligned storage instructions

ABSTRACT

A system and software for improving the performance of processors by incorporating an execution unit operable to decode and execute single instructions in an instruction set comprising (a) group instructions that operate on a plurality of data elements in partitioned fields of a register to produce a catenated result, (b) aligned memory operations that move data between memory and register where the memory operand is aligned, and (c) unaligned memory operations where the memory operand is unaligned.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/436,340filed May 13, 2003, which is a continuation of U.S. patent applicationSer. No. 09/534,745, filed Mar. 24, 2000, now U.S. Pat. No. 6,643,765,which is a continuation of U.S. patent application Ser. No. 09/382,402,filed Aug. 24, 1999, now U.S. Pat. No. 6,295,599, which claims thebenefit of priority to Provisional Application No. 60/097,635 filed Aug.24, 1998, and is a continuation-in-part of U.S. patent application Ser.No. 09/169,963, filed Oct. 13, 1998, now U.S. Pat. No. 6,006,318, whichis a continuation of U.S. patent application Ser. No. 08/754,827, filedNov. 22, 1996, now U.S. Pat. No. 5,822,603, which is a divisional ofU.S. patent application Ser. No. 08/516,036, filed Aug. 16, 1995, nowU.S. Pat. No. 5,742,840, and this application is a continuation of U.S.patent application Ser. No. 09/922,319, filed Aug. 2, 2001 now U.S. Pat.No. 6,725,356, which is a continuation of U.S. patent application Ser.No. 09/382,402, filed Aug. 24, 1999, now U.S. Pat. No. 6,295,599, whichclaims the benefit of priority to Provisional Application No. 60/097,635filed Aug. 24, 1998, and is a continuation-in-part of U.S. patentapplication Ser. No. 09/169,963, filed Oct. 13, 1998, now U.S. Pat. No.6,006,318, which is a continuation of U.S. patent application Ser. No.08/754,827, filed Nov. 22, 1996 now U.S. Pat. No. 5,822,603, which is adivisional of U.S. patent application Ser. No. 08/516,036, filed Aug.16, 1995 now U.S. Pat. No. 5,742,840.

REFERENCE TO PARENT APPLICATIONS

The contents of U.S. patent application Ser. Nos. 09/382,402 and09/922,319 are hereby incorporated by reference including theirappendices in their entirety.

REFERENCE TO AN APPENDIX

This application includes an appendix, submitted herewith The contentsof the appendix are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to general purpose processorarchitectures, and particularly relates to general purpose processorarchitectures capable of executing group operations.

BACKGROUND OF THE INVENTION

The performance level of a processor, and particularly a general purposeprocessor, can be estimated from the multiple of a plurality ofinterdependent factors: clock rate, gates per clock, number of operands,operand and data path width, and operand and data path partitioning.Clock rate is largely influenced by the choice of circuit and logictechnology, but is also influenced by the number of gates per clock.Gates per clock is how many gates in a pipeline may change state in asingle clock cycle. This can be reduced by inserting latches into thedata path: when the number of gates between latches is reduced, a higherclock is possible. However, the additional latches produce a longerpipeline length, and thus come at a cost of increased instructionlatency. The number of operands is straightforward; for example, byadding with carry-save techniques, three values may be added togetherwith little more delay than is required for adding two values. Operandand data path width defines how much data can be processed at once;wider data paths can perform more complex functions, but generally thiscomes at a higher implementation cost. Operand and data pathpartitioning refers to the efficient use of the data path as width isincreased, with the objective of maintaining substantially peak usage.

SUMMARY OF THE INVENTION

Embodiments of the invention pertain to systems and methods forenhancing the utilization of a general purpose processor by addingclasses of instructions. These classes of instructions use the contentsof general purpose registers as data path sources, partition theoperands into symbols of a specified size, perform operations inparallel, catenate the results and place the catenated results into ageneral-purpose register. Some embodiments of the invention relate to ageneral purpose microprocessor which has been optimized for processingand transmitting media data streams through significant parallelism.

Some embodiments of the present invention provide a system and methodfor improving the performance of general purpose processors by includingthe capability to execute group operations involving multiplefloating-point operands. In one embodiment, a programmable mediaprocessor comprises a virtual memory addressing unit, a data path, aregister file comprising a plurality of registers coupled to the datapath, and an execution unit coupled to the data path capable ofexecuting group-floating point operations in which multiplefloating-point operations stored in partitioned fields of one or more ofthe plurality of registers are operated on to produce catenated results.The group floating-point operations may involve operating on at leasttwo of the multiple floating-point operands in parallel. The catenatedresults may be returned to a register, and general purpose registers mayused as operand and result registers for the floating-point operations.In some embodiments the execution unit may also be capable of performinggroup floating-point operations on floating-point data of more than oneprecision. In some embodiments the group floating-point operations mayinclude group add, group subtract, group compare, group multiply andgroup divide arithmetic operations that operate on catenatedfloating-point data. In some embodiments, the group floating-pointoperations may include group multiply-add, group scale-add, and groupset operations that operate on catenated floating-point data.

In one embodiment, the execution unit is also capable of executing groupinteger instructions involving multiple integer operands stored inpartitioned fields of registers. The group integer operations mayinvolve operating on at least two of the multiple integer operands inparallel. The group integer operations may include group add, groupsubtract, group compare, and group multiply arithmetic operations thatoperate on catenated integer data.

In one embodiment, the execution unit is capable of performing groupdata handling operations, including operations that copy, operationsthat shift, operations that rearrange and operations that resizecatenated integer data stored in a register and return catenatedresults. The execution unit may also be configurable to perform groupdata handling operations on integer data having a symbol width of 8bits, group data handling operations on integer data having a symbolwidth of 16 bits, and group data handling operations on integer datahaving a symbol width of 32 bits. In one embodiment, the operations arecontrolled by values in a register operand. In one embodiment, theoperations are controlled by values in the instruction.

In one embodiment, the multi-precision execution unit is capable ofexecuting a Galois field instruction operation.

In one embodiment, the multi-precision execution unit is configurable toexecute a plurality of instruction streams in parallel from a pluralityof threads, and the programmable media processor further comprises aregister file associated with each thread executing in parallel on themulti-precision execution unit to support processing of the plurality ofthreads. In some embodiments, the multi-precision execution unitexecutes instructions from the plurality of instruction streams in around-robin manner. In some embodiments, the processor ensures only onethread from the plurality of threads can handle an exception at anygiven time.

Some embodiments of the present invention provide a multiplier arraythat is fully used for high precision arithmetic, but is only partlyused for other, lower precision operations. This can be accomplished byextracting the high-order portion of the multiplier product or sum ofproducts, adjusted by a dynamic shift amount from a general register oran adjustment specified as part of the instruction, and rounded by acontrol value from a register or instruction portion. The rounding maybe any of several types, including round-to-nearest/even; toward zero,floor, or ceiling. Overflows are typically handled by limiting theresult to the largest and smallest values that can be accuratelyrepresented in the output result.

When an extract is controlled by a register, the size of the result canbe specified, allowing rounding and limiting to a smaller number of bitsthan can fit in the result. This permits the result to be scaled for usein subsequent operations without concern of overflow or rounding. As aresult, performance is enhanced. In those instances where the extract iscontrolled by a register, a single register value defines the size ofthe operands, the shift amount and size of the result, and the roundingcontrol. By placing such control information in a single register, thesize of the instruction is reduced over the number of bits that such aninstruction would otherwise require, again improving performance andenhancing processor flexibility. Exemplary instructions are EnsembleConvolve Extract, Ensemble Multiply Extract, Ensemble Multiply AddExtract, and Ensemble Scale Add Extract. With particular regard to theEnsemble Scale Add Extract Instruction, the extract control informationis combined in a register with two values used as scalar multipliers tothe contents of two vector multiplicands. This combination reduces thenumber of registers otherwise required, thus reducing the number of bitsrequired for the instruction.

In one embodiment, the processor performs load and store instructionsoperable to move values between registers and memory. In one embodiment,the processor performs both instructions that verify alignment of memoryoperands and instructions that permit memory operands to be unaligned.In one embodiment, the processor performs store multiplex instructionsoperable to move to memory a portion of data contents controlled by acorresponding mask contents. In one embodiment, this masked storageoperation is performed by indivisibly reading-modifying-writing a memoryoperand.

In one embodiment, all processor, memory and interface resources aredirectly accessible to high-level language programs. In one embodiment,assembler codes and high-level language formats are specified to accessenhanced instructions. In one embodiment interface and system state ismemory mapped, so that it can be manipulated by compiled code. In oneembodiment, software libraries provide other operations required by theANSI/IEEE floating-point standard. In one embodiment, softwareconventions are employed at software module boundaries, in order topermit the combination of separately compiled code and to providestandard interfaces between application, library and system software. Inone embodiment, instruction scheduling is performed by a compiler.

THE FIGURES

FIG. 1 is a system level diagram showing the functional blocks of asystem according to the present invention.

FIG. 2 is a matrix representation of a wide matrix multiply inaccordance with one embodiment of the present invention.

FIG. 3 is a further representation of a wide matrix multiple inaccordance with one embodiment of the present invention.

FIG. 4 is a system level diagram showing the functional blocks of asystem incorporating a combined Simultaneous Multi Threading andDecoupled Access from Execution processor in accordance with oneembodiment of the present invention.

FIG. 5 illustrates a wide operand in accordance with one embodiment ofthe present invention.

FIG. 6 illustrates an approach to specifier decoding in accordance withone embodiment of the present invention.

FIG. 7 illustrates in operational block form a Wide Function Unit inaccordance with one embodiment of the present invention.

FIG. 8 illustrates in flow diagram form the Wide Microcache controlfunction.

FIG. 9 illustrates Wide Microcache data structures.

FIGS. 10 and 11 illustrate a Wide Microcache control.

FIG. 12 is a timing diagram of a decoupled pipeline structure inaccordance with one embodiment of the present invention.

FIG. 13 further illustrates the pipeline organization of FIG. 12.

FIG. 14 is a diagram illustrating the basic organization of the memorymanagement system according to the present embodiment of the invention.

FIG. 15 illustrates the physical address of an LTB entry for thread th,entry en, byte b.

FIG. 16 illustrates a definition for AccessPhysicalLTB.

FIG. 17 illustrates how various 16-bit values are packed together into a64-bit LTB entry.

FIG. 18 illustrates global access as fields of a control register.

FIG. 19 shows how a single-set LTB context may be further simplified byreserving the implementation of the lm and la registers.

FIG. 20 shows the partitioning of the virtual address space if thelargest possible space is reserved for an address space identifier.

FIG. 21 shows how the LTB protect field controls the minimum privilegelevel required for each memory action of read (r), write (w), execute(x), and gateway (g), as well as memory and cache attributes of writeallocate (wa), detail access (da), strong ordering (so), cache disable(cd), and write through (wt).

FIG. 22 illustrates a definition for LocalTranslation.

FIG. 23 shows how the low-order GT bits of the th value are ignored,reflecting that 2GT threads share a single GTB.

FIG. 24 illustrates a definition for AccessPhysicalGTB.

FIG. 25 illustrates the format of a GTB entry.

FIG. 26 illustrates a definition for GlobalAddressTranslation.

FIG. 27 illustrates a definition for GTBUpdateWrite.

FIG. 28 shows how the low-order GT bits of the th value are ignored,reflecting that 2GT threads share single GTB registers.

FIG. 29 illustrates the registers GTBLast, GTBFirst, and GTBBump.

FIG. 30 illustrates a definition for AccessPhysicalGTBRegisters.

FIGS. 31A-31C illustrate Group Boolean instructions in accordance withan exemplary embodiment of the present invention.

FIGS. 31D-31E illustrate Group Multiplex instructions in accordance withan exemplary embodiment of the present invention.

FIGS. 32A-32C illustrate Group Add instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 33A-33C illustrate Group Subtract and Group Set instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 34A-34C illustrate Ensemble Divide and Ensemble Multiplyinstructions in accordance with an exemplary embodiment of the presentinvention.

FIGS. 35A-35C illustrate Group Compare instructions in accordance withan exemplary embodiment of the present invention.

FIGS. 36A-36C illustrate Ensemble Unary instructions in accordance withan exemplary embodiment of the present invention.

FIG. 37 illustrates exemplary functions that are defined for use withinthe detailed instruction definitions in other sections.

FIGS. 38A-38C illustrate Ensemble Floating-Point Add, EnsembleFloating-Point Divide, and Ensemble Floating-Point Multiply instructionsin accordance with an exemplary embodiment of the present invention.

FIGS. 38D-38F illustrate Ensemble Floating-Point Multiply Addinstructions in accordance with an exemplary embodiment of the presentinvention.

FIGS. 38G-38I illustrate Ensemble Floating-Point Scale Add instructionsin accordance with an exemplary embodiment of the present invention.

FIGS. 39A-39C illustrate Ensemble Floating-Point Subtract instructionsin accordance with an exemplary embodiment of the present invention.

FIGS. 39D-39G illustrate Group Set Floating-point instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 40A-40C illustrate Group Compare Floating-point instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 41A-41C illustrate Ensemble Unary Floating-point instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 42A-42D illustrate Ensemble Multiply Galois Field instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 43A-43D illustrate Compress, Expand, Rotate, and Shiftinstructions in accordance with an exemplary embodiment of the presentinvention.

FIGS. 43E-43G illustrate Shift Merge instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 43H-43J illustrate Compress Immediate, Expand Immediate, RotateImmediate, and Shift Immediate instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 43K-43M illustrate Shift Merge Immediate instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 44A-44D illustrate Extract instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 44E-44G illustrate Ensemble Extract instructions in accordancewith an exemplary embodiment of the present invention.

FIGS. 45A-45F illustrate Deposit and Withdraw instructions in accordancewith an exemplary embodiment of the present invention.

FIGS. 45G-45J illustrate Deposit Merge instructions in accordance withan exemplary embodiment of the present invention.

FIGS. 46A-46E illustrate Shuffle instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 47A-47C illustrate Swizzle instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 47D-47E illustrate Select instructions in accordance with anexemplary embodiment of the present invention.

FIG. 48 is a pin summary describing the functions of various pins inaccordance with the one embodiment of the present invention.

FIGS. 49A-49G present electrical specifications describing AC and DCparameters in accordance with one embodiment of the present invention.

FIGS. 50A-50C illustrate Load instructions in accordance with anexemplary embodiment of the present invention.

FIGS. 51A-51C illustrate Load Immediate instructions in accordance withan exemplary embodiment of the present invention.

FIGS. 52A-52C illustrate Store and Store Multiplex instructions inaccordance with an exemplary embodiment of the present invention.

FIGS. 53A-53C illustrate Store Immediate and Store Multiplex Immediateinstructions in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, a general purpose processor is illustratedtherein in block diagram form. In FIG. 1, four copies of an access unitare shown, each with an access instruction fetch queue A-Queue 101-104.Each access instruction fetch queue A-Queue 101104 is coupled to anaccess register file AR 105-108, which are each coupled to two accessfunctional units A 109-116. In a typical embodiment, each thread of theprocessor may have on the order of sixty-four general purpose registers(e.g., the AR's 105-108 and ER's 125-128). The access units functionindependently for four simultaneous threads of execution, and eachcompute program control flow by performing arithmetic and branchinstructions and access memory by performing load and storeinstructions. These access units also provide wide operand specifiersfor wide operand instructions. These eight access functional units A109-116 produce results for access register files AR 105-108 and memoryaddresses to a shared memory system 117-120.

In one embodiment, the memory hierarchy includes on-chip instruction anddata memories, instruction and data caches, a virtual memory facility,and interfaces to external devices. In FIG. 1, the memory system iscomprised of a combined cache and niche memory 117, an external businterface 118, and, externally to the device, a secondary cache 119 andmain memory system with 1/O devices 120. The memory contents fetchedfrom memory system 117-120 are combined with execute instructions notperformed by the access unit, and entered into the four executeinstruction queues E-Queue 121-124. In accordance with one embodiment ofthe present invention, from the software perspective, the machine stateincludes a linear byte-addressed shared memory space. For wideinstructions, memory contents fetched from memory system 117-120 arealso provided to wide operand microcaches 132-136 by bus 137.Instructions and memory data from E-queue 121-124 are presented toexecution register files 125-128, which fetch execution register filesource operands. The instructions are coupled to the execution unitarbitration unit Arbitration 131, that selects which instructions fromthe four threads are to be routed to the available execution functionalunits E 141 and 149, X 142 and 148, G 143-144 and 146-147, and T 145.The execution functional units E 141 and 149, the execution functionalunits X 142 and 148, and the execution functional unit T 145 eachcontain a wide operand microcache 132-136, which are each coupled to thememory system 117 by bus 137.

The execution functional units G 143-144 and 146-147 are grouparithmetic and logical units that perform simple arithmetic and logicalinstructions, including group operations wherein the source and resultoperands represent a group of values of a specified symbol size, whichare partitioned and operated on separately, with results catenatedtogether. In a presently preferred embodiment the data path is 128 bitswide, although the present invention is not intended to be limited toany specific size of data path.

The execution functional units X 142 and 148 are crossbar switch unitsthat perform crossbar switch instructions. The crossbar switch units 142and 148 perform data handling operations on the data stream providedover the data path source operand buses 151-158, including deal,shuffles, shifts, expands, compresses, swizzles, permutes and reverses,plus the wide operations discussed hereinafter. In a key element of afirst aspect of the invention, at least one such operation will beexpanded to a width greater than the general register and data pathwidth. Examples of the data manipulation operations are described in theAppendix included herewith.

The execution functional units E 141 and 149 are ensemble units thatperform ensemble instructions using a large array multiplier, includinggroup or vector multiply and matrix multiply of operands partitionedfrom data path source operand buses 151-158 and treated as integer,floating-point, polynomial or Galois field values. According to thepresent embodiment of the invention, a general software solution isprovided to the most common operations required for Galois Fieldarithmetic. The instructions provided include a polynomial multiply,with the polynomial specified as one register operand. This instructioncan be used to perform CRC generation and checking, Reed-Solomon codegeneration and checking, and spread-spectrum encoding and decoding.Also, matrix multiply instructions and other operations described in theAppendix included herewith utilize a wide operand loaded into the wideoperand microcache 132 and 136.

The execution functional unit T 145 is a translate unit that performstable-look-up operations on a group of operands partitioned from aregister operand, and catenates the result. The Wide Translateinstruction described in the Appendix included herewith utilizes a wideoperand loaded into the wide operand microcache 134.

The execution functional units E 141, 149, execution functional unitsX-142 148, and execution functional unit T each contain dedicatedstorage to permit storage of source operands including wide operands asdiscussed hereinafter. The dedicated storage 132-136, which may bethought of as a wide microcache, typically has a width which is amultiple of the width of the data path operands related to the data pathsource operand buses 151-158. Thus, if the width of the data path151-158 is 128 bits, the dedicated storage 132-136 may have a width of256, 512, 1024 or 2048 bits. Operands which utilize the full width ofthe dedicated storage are referred to herein as wide operands, althoughit is not necessary in all instances that a wide operand use theentirety of the width of the dedicated storage; it is sufficient thatthe wide operand use a portion greater than the width of the memory datapath of the output of the memory system 117-120 and the functional unitdata path of the input of the execution functional units 141-149, thoughnot necessarily greater than the width of the two combined. Because thewidth of the dedicated storage 132-136 is greater than the width of thememory operand bus 137, portions of wide operands are loadedsequentially into the dedicated storage 132-136. However, once loaded,the wide operands may then be used at substantially the same time. Itcan be seen that functional units 141-149 and associated executionregisters 125-128 form a data functional unit, the exact elements ofwhich may vary with implementation.

The execution register file ER 125-128 source operands are coupled tothe execution units 141-145 using source operand buses 151-154 and tothe execution units 145-149 using source operand buses 155-158. Thefunction unit result operands from execution units 141145 are coupled tothe execution register file ER 125-128 using result bus 161 and thefunction units result operands from execution units 145-149 are coupledto the execution register file using result bus 162.

The wide operands used in some embodiments of the present inventionprovide the ability to execute complex instructions such as the widemultiply matrix instruction shown in FIG. 2, which can be appreciated inan alternative form, as well, from FIG. 3. As can be appreciated fromFIGS. 2 and 3, a wide operand permits, for example, the matrixmultiplication of various sizes and shapes which exceed the data pathwidth. The example of FIG. 2 involves a matrix specified by register rchaving a 128*64/size multiplied by a vector contained in register rbhaving a 128 size, to yield a result, placed in register rd, of 128bits.

The operands that are substantially larger than the data path width ofthe processor are provided by using a general-purpose register tospecify a memory specifier from which more than one but in someembodiments several data path widths of data can be read into thededicated storage. The memory specifier typically includes the memoryaddress together with the size and shape of the matrix of data beingoperated on. The memory specifier or wide operand specifier can bebetter appreciated from FIG. 5, in which a specifier 500 is seen to bean address, plus a field representative of the size/2 and a furtherfield representative of width/2, where size is the product of the depthand width of the data. The address is aligned to a specified size, forexample sixty-four bytes, so that a plurality of low order bits (forexample, six bits) are zero. The specifier 500 can thus be seen tocomprise a first field 505 for the address, plus two field indicia 510within the low order six bits to indicate size and width.

The decoding of the specifier 500 may be further appreciated from FIG. 6where, for a given specifier 600 made up of an address field 605together with a field 610 comprising plurality of low order bits. By aseries of arithmetic operations shown at steps 615 and 620, the portionof the field 610 representative of width/2 is developed. In a similarseries of steps shown at 625 and 630, the value of t is decoded, whichcan then be used to decode both size and address. The portion of thefield 610 representative of size/2 is decoded as shown at steps 635 and640, while the address is decoded in a similar way at steps 645 and 650.

The wide function unit may be better appreciated from FIG. 7, in which aregister number 700 is provided to an operand checker 705. Wide operand,specifier 710 communicates with the operand checker 705 and alsoaddresses memory 715 having a defined memory width. The memory addressincludes a plurality of register operands 720A-n, which are accumulatedin a dedicated storage portion 714 of a data functional unit 725. In theexemplary embodiment shown in FIG. 7, the dedicated storage 714 can beseen to have a width equal to eight data path widths, such that eightwide operand portions 730A-H are sequentially loaded into the dedicatedstorage to form the wide operand. Although eight portions are shown inFIG. 7, the present invention is not limited to eight or any otherspecific multiple of data path widths. Once the wide operand portions730A-H are sequentially loaded, they may be used as a single wideoperand 735 by the functional element 740, which may be any element(s)from FIG. 1 connected thereto. The result of the wide operand is thenprovided. to a result register 745, which in a presently preferredembodiment is of the same width as the memory width.

Once the wide operand is successfully loaded into the dedicated storage714, a second aspect of the present invention may be appreciated.Further execution of this instruction or other similar instructions thatspecify the same memory address can read the dedicated storage to obtainthe operand value under specific conditions that determine whether thememory operand has been altered by intervening instructions. Assumingthat these conditions are met, the memory operand fetch from thededicated storage is combined with one or more register operands in thefunctional unit, producing a result. In some embodiments, the size ofthe result is limited to that of a general register, so that no similardedicated storage is required for the result. However, in some differentembodiments, the result may be a wide operand, to further enhanceperformance.

To permit the wide operand value to be addressed by subsequentinstructions specifying the same memory address, various conditions mustbe checked and confirmed:

Those conditions include:

-   1. Each memory store instruction checks the memory address against    the memory addresses recorded for the dedicated storage. Any match    causes the storage to be marked invalid, since a memory store    instruction directed to any of the memory addresses stored in    dedicated storage 714 means that data has been overwritten.-   2. The register number used to address the storage is recorded. If    no intervening instructions have written to the register, and the    same register is used on the subsequent instruction, the storage is    valid (unless marked invalid by rule #1).-   3. If the register has been modified or a different register number    is used, the value of the register is read and compared against the    address recorded for the dedicated storage. This uses more resources    than #1 because of the need to fetch the register contents and    because the width of the register is greater than that of the    register number itself. If the address matches, the storage is    valid. The new register number is recorded for the dedicated    storage.

If conditions #2 or #3 are not met, the register contents are used toaddress the general-purpose processor's memory and load the dedicatedstorage. If dedicated storage is already fully loaded, a portion of thededicated storage must be discarded (victimized) to make room for thenew value. The instruction is then performed using the newly updateddedicated storage. The address and register number is recorded for thededicated storage.

By checking the above conditions, the need for saving and restoring thededicated storage is eliminated. In addition, if the context of theprocessor is changed and the new context does not employ Wideinstructions that reference the same dedicated storage, when theoriginal context is restored, the contents of the dedicated storage areallowed to be used without refreshing the value from memory, usingchecking rule #3. Because the values in the dedicated storage are readfrom memory and not modified directly by performing wide operations, thevalues can be discarded at any time without saving the results intogeneral memory. This property simplifies the implementation of rule #4above.

An alternate embodiment of the present invention can replace rule #1above with the following rule:

-   1a. Each memory store instruction checks the memory address against    the memory addresses recorded for the dedicated storage. Any match    causes the dedicated storage to be updated, as well as the general    memory.

By use of the above rule 1.a, memory store instructions can modify thededicated storage, updating just the piece of the dedicated storage thathas been changed, leaving the remainder intact. By continuing to updatethe general memory, it is still true that the contents of the dedicatedmemory can be discarded at any time without saving the results intogeneral memory. Thus rule #4 is not made more complicated by thischoice. The advantage of this alternate embodiment is that the dedicatedstorage need not be discarded (invalidated) by memory store operations.

Referring next to FIG. 9, an exemplary arrangement of the datastructures of the wide microcache or dedicated storage 114 may be betterappreciated. The wide microcache contents, wmc.c, can be seen to form aplurality of data path widths 900A-n, although in the example shown thenumber is eight. The physical address, wmc.pa, is shown as 64 bits inthe example shown, although the invention is not limited to a specificwidth. The size of the contents, wmc.size, is also provided in a fieldwhich is shown as 10 bits in an exemplary embodiment. A “contents valid”flag, wmc.ev, of one bit is also included in the data structure,together with a two bit field for thread last used, or wmc.th. Inaddition, a six bit field for register last used, wmc.reg, is providedin an exemplary embodiment. Further, a one bit flag for register andthread valid, or wmc.rtv, may be provided.

The process by which the microcache is initially written with a wideoperand, and thereafter verified as valid for fast subsequentoperations, may be better appreciated from FIG. 8. The process begins at800, and progresses to step 805 where a check of the register contentsis made against the stored value wmc.rc. If true, a check is made atstep 810 to verify the thread. If true, the process then advances tostep 815 to verify whether the register and thread are valid. If step815 reports as true, a check is made at step 820 to verify whether thecontents are valid. If all of steps 805 through 820 return as true, thesubsequent instruction is able to utilize the existing wide operand asshown at step 825, after which the process ends. However, if any ofsteps 805 through 820 return as false, the process branches to step 830,where content, physical address and size are set. Because steps 805through 820 all lead to either step 825 or 830, steps 805 through 820may be performed in any order or simultaneously without altering theprocess. The process then advances to step 835 where size is checked.This check basically ensures that the size of the translation unit isgreater than or equal to the size of the wide operand, so that aphysical address can directly replace the use of a virtual address. Theconcern is that, in some embodiments, the wide operands may be largerthan the minimum region that the virtual memory system is capable ofmapping. As a result, it would be possible for a single contiguousvirtual address range to be mapped into multiple, disjoint physicaladdress ranges, complicating the task of comparing physical addresses.By determining the size of the wide operand and comparing that sizeagainst the size of the virtual address mapping region which isreferenced, the instruction is aborted with an exception trap if thewide operand is larger than the mapping region. This ensures secureoperation of the processor. Software can then re-map the region using alarger size map to continue execution if desired. Thus, if size isreported as unacceptable at step 835, an exception is generated at step840. If size is acceptable, the process advances to step 845 wherephysical address is checked. If the check reports as met, the processadvances to step 850, where a check of the contents valid flag is made.If either check at step 845 or 850 reports as false, the processbranches and new content is written into the dedicated storage 114, withthe fields thereof being set accordingly. Whether the check at step 850reported true, or whether new content was written at step 855, theprocess advances to step 860 where appropriate fields are set toindicate the validity of the data, after which the requested functioncan be performed at step 825. The process then ends.

Referring next to FIGS. 10 and 11, which together show the operation ofthe microcache controller from a hardware standpoint, the operation ofthe microcache controller may be better understood. In the hardwareimplementation, it is clear that conditions which are indicated assequential steps in FIGS. 8 and 9 above can be performed in parallel,reducing the delay for such wide operand checking. Further, a copy ofthe indicated hardware may be included for each wide microcache, andthereby all such microcaches as may be alternatively referenced by aninstruction can be tested in parallel. It is believed that no furtherdiscussion of FIGS. 10 and 11 is required in view of the extensivediscussion of FIGS. 8 and 9, above.

Various alternatives to the foregoing approach do exist for the use ofwide operands, including an implementation in which a single instructioncan accept two wide operands, partition the operands into symbols,multiply corresponding symbols together, and add the products to producea single scalar value or a vector of partitioned values of width of theregister file, possibly after extraction of a portion of the sums. Suchan instruction can be valuable for detection of motion or estimation ofmotion in video compression. A further enhancement of such aninstruction can incrementally update the dedicated storage if theaddress of one wide operand is within the range of previously specifiedwide operands in the dedicated storage, by loading only the portion notalready within the range and shifting the in-range portion as required.Such an enhancement allows the operation to be performed over a “slidingwindow” of possible values. In such an instruction, one wide operand isaligned and supplies the size and shape information, while the secondwide operand, updated incrementally, is not aligned.

Another alternative embodiment of the present invention can defineadditional instructions where the result operand is a wide operand. Suchan enhancement removes the limit that a result can be no larger than thesize of a general register, further enhancing performance. These wideresults can be cached locally to the functional unit that created them,but must be copied to the general memory system before the storage canbe reused and before the virtual memory system alters the mapping of theaddress of the wide result. Data paths must be added so that loadoperations and other wide operations can read these wideresults—forwarding of a wide result from the output of a functional unitback to its input is relatively easy, but additional data paths may haveto be introduced if it is desired to forward wide results back to otherfunctional units as wide operands.

As previously discussed, a specification of the size and shape of thememory operand is included in the low-order bits of the address. In apresently preferred implementation, such memory operands are typically apower of two in size and aligned to that size. Generally, one-half thetotal size is added (or inclusively or'ed, or exclusively or'ed) to thememory address, and one half of the data width is added (or inclusivelyor'ed, or exclusively or'ed) to the memory address. These bits can bedecoded and stripped from the memory address, so that the controller ismade to step through all the required addresses. This decreases thenumber of distinct operands required for these instructions, as thesize, shape and address of the memory operand are combined into a singleregister operand value.

Particular examples of wide operations which are defined by the presentinvention include the Wide Switch instruction that performs bit-levelswitching; the Wide Translate instruction which performs byte (orlarger) table-lookup; Wide Multiply Matrix, Wide Multiply Matrix Extractand Wide Multiply Matrix Extract Immediate (discussed below), WideMultiply Matrix Floating-point, and Wide Multiply Matrix Galois (alsodiscussed below). While the discussion below focuses on particular sizesfor the exemplary instructions, it will be appreciated that theinvention is not limited to a particular width.

The Wide Switch instruction rearranges the contents of up to tworegisters (256 bits) at the bit level, producing a full-width (128 bits)register result. To control the rearrangement, a wide operand specifiedby a single register, consisting of eight bits per bit position is used.For each result bit position, eight wide operand bits for each bitposition select which of the 256 possible source register bits to placein the result. When a wide operand size smaller than 128 bytes, the highorder bits of the memory operand are replaced with values correspondingto the result bit position, so that the memory operand specifies a bitselection within symbols of the operand size, performing the sameoperation on each symbol.

The Wide Translate instructions use a wide operand to specify a table ofdepth up to 256 entries and width of up to 128 bits. The contents of aregister is partitioned into operands of one, two, four, or eight bytes,and the partitions are used to select values from the table in parallel.The depth and width of the table can be selected by specifying the sizeand shape of the wide operand as described above.

The Wide Multiply Matrix instructions use a wide operand to specify amatrix of values of width up to 64 bits (one half of register file anddata path width) and depth of up to 128 bits/symbol size. The contentsof a general register (128 bits) is used as a source operand,partitioned into a vector of symbols, and multiplied with the matrix,producing a vector of width up to 128 bits of symbols of twice the sizeof the source operand symbols. The width and depth of the matrix can beselected by specifying the size and shape of the wide operand asdescribed above. Controls within the instruction allow specification ofsigned, mixed-signed, unsigned, complex, or polynomial operands.

The Wide Multiply Matrix Extract instructions use a wide operand tospecify a matrix of value of width up to 128 bits (full width ofregister file and data path) and depth of up to 128 bits/symbol size.The contents of a general register (128 bits) is used as a sourceoperand, partitioned into a vector of symbols, and multiplied with thematrix, producing a vector of width up to 256 bits of symbols of twicethe size of the source operand symbols plus additional bits to representthe sums of products without overflow. The results are then extracted ina manner described below (Enhanced Multiply Bandwidth by ResultExtraction), as controlled by the contents of a general registerspecified by the instruction. The general register also specifies theformat of the operands: signed, mixed-signed, unsigned, and complex aswell as the size of the operands, byte (8 bit), doublet (16 bit),quadlet (32 bit), or hexlet (64 bit).

The Wide Multiply Matrix Extract Immediate instructions perform the samefunction as above, except that the extraction, operand format and sizeis controlled by fields in the instruction. This form encodes commonforms of the above instruction without the need to initialize a registerwith the required control information. Controls within the instructionallow specification of signed, mixed-signed, unsigned, and complexoperands.

The Wide Multiply Matrix Floating-point instructions perform a matrixmultiply in the same form as above, except that the multiplies andadditions are performed in floating-point arithmetic. Sizes of half(16-bit), single (32-bit), double (64-bit), and complex sizes of half,single and double can be specified within the instruction.

Wide Multiply Matrix Galois instructions perform a matrix multiply inthe same form as above, except that the multiples and additions areperformed in Galois field arithmetic. A size of 8 bits can be specifiedwithin the instruction. The contents of a general register specify thepolynomial with which to perform the Galois field remainder operation.The nature of the matrix multiplication is novel and described in detailbelow.

In another aspect of the invention, memory operands of eitherlittle-endian or big-endian conventional byte ordering are facilitated.Consequently, all Wide operand instructions are specified in two forms,one for little-endian byte ordering and one for big-endian byteordering, as specified by a portion of the instruction. The byte orderspecifies to the memory system the order in which to deliver the byteswithin units of the data path width (128 bits), as well as the order toplace multiple memory words (128 bits) within a larger Wide operand.Each of these instructions is described in greater detail in theAppendix filed herewith.

Some embodiments of the present invention address extraction of a highorder portion of a multiplier product or sum of products, as a way ofefficiently utilizing a large multiplier array. Parent U.S. Pat. No.5,742,840 and U.S. Pat. No. 5,953,241 describe a system and method forenhancing the utilization of a multiplier array by adding specificclasses of instructions to a general-purpose processor. This addressesthe problem of making the most use of a large multiplier array that isfully used for high-precision arithmetic—for example a 64×64 bitmultiplier is fully used by a 64-bit by 64-bit multiply, but only onequarter used for a 32-bit by 32-bit multiply) for (relative to themultiplier data width and registers) low-precision arithmeticoperations. In particular, operations that perform a great manylow-precision multiplies which are combined (added) together in variousways are specified. One of the overriding considerations in selectingthe set of operations is a limitation on the size of the result operand.In an exemplary embodiment, for example, this size might be limited toon the order of 128 bits, or a single register, although no specificsize limitation need exist.

The size of a multiply result, a product, is generally the sum of thesizes of the operands, multiplicands and multiplier. Consequently,multiply instructions specify operations in which the size of the resultis twice the size of identically-sized input operands. For our prior artdesign, for example, a multiply instruction accepted two 64-bit registersources and produces a single 128-bit register-pair result, using anentire 64×64 multiplier array for 64-bit symbols, or half the multiplierarray for pairs of 32-bit symbols, or one-quarter the multiplier arrayfor quads of 16-bit symbols. For all of these cases, note that tworegister sources of 64 bits are combined, yielding a 128-bit result.

In several of the operations, including complex multiplies, convolve,and matrix multiplication, low-precision multiplier products are addedtogether. The additions further increase the required precision. The sumof two products requires one additional bit of precision; adding fourproducts requires two, adding eight products requires three, addingsixteen products requires four. In some prior designs, some of thisprecision is lost, requiring scaling of the multiplier operands to avoidoverflow, further reducing accuracy of the result.

The use of register pairs creates an undesirable complexity, in thatboth the register pair and individual register values must be bypassedto subsequent instructions. As a result, with prior art techniques onlyhalf of the source operand 128-bit register values could be employedtoward producing a single-register 128-bit result.

In some embodiments of the present invention, a high-order portion ofthe multiplier product or sum of products is extracted, adjusted by adynamic shift amount from a general register or an adjustment specifiedas part of the instruction, and, rounded by a control value from aregister or instruction portion as round-to-nearest/even, toward zero,floor, or ceiling. Overflows are handled by limiting the result to thelargest and smallest values that can be accurately represented in theoutput result. This operation is more fully described in the attachedAppendix.

In the present invention, when the extract is controlled by a register,the size of the result can be specified, allowing rounding and limitingto a smaller number of bits than can fit in the result. This permits theresult to be scaled to be used in subsequent operations without concernof overflow or rounding, enhancing performance.

Also in the present invention, when the extract is controlled by aregister, a single register value defines the size of the operands, theshift amount and size of the result, and the rounding control. Byplacing all this control information in a single register, the size ofthe instruction is reduced over the number of bits that such ainstruction would otherwise require, improving performance and enhancingflexibility of the processor.

The particular instructions included in this aspect of the presentinvention are Ensemble Convolve Extract, Ensemble Multiply Extract,Ensemble Multiply Add Extract and Ensemble Scale Add Extract, each ofwhich is more thoroughly treated in the appendix.

An aspect of the present invention defines the Ensemble Scale AddExtract instruction, that combines the extract control information in aregister along with two values that are used as scalar multipliers tothe contents of two vector multiplicands. This combination reduces thenumber of registers that would otherwise be required, or the number ofbits that the instruction would otherwise require, improvingperformance.

Several of these instructions (Ensemble Convolve Extract, EnsembleMultiply Add Extract) are typically available only in forms where theextract is specified as part of the instruction. An alternativeembodiment can incorporate forms of the operations in which the size ofthe operand, the shift amount and the rounding can be controlled by thecontents of a general register (as they are in the Ensemble MultiplyExtract instruction). The definition of this kind of instruction forEnsemble Convolve Extract, and Ensemble Multiply Add Extract wouldrequire four source registers, which increases complexity by requiringadditional general-register read ports.

Another alternative embodiment can reduce the number of registerread-ports required for implementation of instructions in which thesize, shift and rounding of operands is controlled by a register. Thevalue of the extract control register can be fetched using an additionalcycle on an initial execution and retained within or near the functionalunit for subsequent executions, thus reducing the amount of hardwarerequired for implementation with a small additional performance penalty.The value retained would be marked invalid, causing a re-fetch of theextract control register, by instructions that modify the register, oralternatively, the retained value can be updated by such an operation. Are-fetch of the extract control register would also be required if adifferent register number were specified on a subsequent execution. Itshould be clear that the properties of the above two alternativeembodiments can be combined.

Another embodiment of the invention includes Galois field arithmetic,where multiplies are performed by an initial binary polynomialmultiplication (unsigned binary multiplication with carries suppressed),followed by a polynomial modulo/remainder operation (unsigned binarydivision with carries suppressed). The remainder operation is relativelyexpensive in area and delay. In Galois field arithmetic, additions areperformed by binary addition with carries suppressed, or equivalently, abitwise exclusive-or operation. In this aspect of the present invention,a matrix multiplication is performed using Galois field arithmetic,where the multiplies and additions are Galois field multiples andadditions.

Using prior art methods, a 16 byte vector multiplied by a 16×16 bytematrix can be performed as 256 8-bit Galois field multiplies and16*15=240 8-bit Galois field additions. Included in the 256 Galois fieldmultiplies are 256 polynomial multiplies and 256 polynomial remainderoperations. But by use of the present invention, the total computationcan be reduced significantly by performing 256 polynomial multiplies,240 16-bit polynomial additions, and 16 polynomial remainder operations.Note that the cost of the polynomial additions has been doubled, asthese are now 16-bit operations, but the cost of the polynomialremainder functions has been reduced by a factor of 16. Overall, this isa favorable tradeoff, as the cost of addition is much lower than thecost of remainder.

In a still further aspect of the present invention, a technique isprovided for incorporating floating point information into processorinstructions. In U.S. Pat. No. 5,812,439, a system and method aredescribed for incorporating control of rounding and exceptions forfloating-point instructions into the instruction itself. The presentinvention extends this invention to include separate instructions inwhich rounding is specified, but default handling of exceptions is alsospecified, for a particular class of floating-point instructions.Specifically, the SINK instruction (which converts floating-point valuesto integral values) is available with control in the instruction thatinclude all previously specified combinations (default-near rounding anddefault exceptions, Z—round-toward-zero and trap on exceptions, N—roundto nearest and trap on exceptions, F—floor rounding (toward minusinfinity) and trap on exceptions, C—ceiling rounding (toward plusinfinity) and trap on exceptions, and X—trap on inexact and otherexceptions), as well as three new combinations (Z.D—round toward zeroand default exception handling, F.D—floor rounding and default exceptionhandling, and C.D—ceiling rounding and default exception handling). (Theother combinations: N.D is equivalent to the default, and X.D—trap oninexact but default handling for other exceptions is possible but notparticularly valuable).

Pipelining and Multithreading

As shown in FIG. 4, some embodiments of the present invention employboth decoupled access from execution pipelines and simultaneousmultithreading in a unique way. Simultaneous Multithreaded pipelineshave been employed in prior art to enhance the utilization of data pathunits by allowing instructions to be issued from one of severalexecution threads to each functional unit (e.g., Susan Eggers,University of Wash, papers on Simultaneous Multithreading).

Decoupled access from execution pipelines have been employed in priorart to enhance the utilization of execution data path units by bufferingresults from an access unit, which computes addresses to a memory unitthat in turn fetches the requested items from memory, and thenpresenting them to an execution unit (e.g., James E. Smith, paper onDecoupled Access from Execution).

Compared to conventional pipelines, Eggers prior art used an additionalpipeline cycle before instructions could be issued to functional units,the additional cycle needed to determine which threads should bepermitted to issue instructions. Consequently, relative to conventionalpipelines, the prior art design had additional delay, includingdependent branch delay.

The embodiment shown in FIG. 4 contains individual access data pathunits, with associated register files, for each execution thread. Theseaccess units produce addresses, which are aggregated together to acommon memory unit, which fetches all the addresses and places thememory contents in one or more buffers. Instructions for executionunits, which are shared to varying degrees among the threads are alsobuffered for later execution. The execution units then performoperations from all active threads using functional data path units thatare shared.

For instructions performed by the execution units, the extra cyclerequired for prior art simultaneous multithreading designs is overlappedwith the memory data access time from prior art decoupled access fromexecution cycles, so that no additional delay is incurred by theexecution functional units for scheduling resources. For instructionsperformed by the access units, by employing individual access units foreach thread the additional cycle for scheduling shared resources is alsoeliminated.

This is a favorable tradeoff because, while threads do not share theaccess functional units, these units are relatively small compared tothe execution functional units, which are shared by threads.

FIG. 12 is a timing diagram of a decoupled pipeline structure inaccordance with one embodiment of the present invention. As illustratedin FIG. 12, the time permitted by a pipeline to service load operationsmay be flexibly extended. Here, various types of instructions areabbreviated as A, L, B, E, and S, representing a register-to-registeraddress calculation, a memory load, a branch, a register-to-registerdata calculation, and a memory store, respectively. According to thepresent embodiment, the front of the pipeline, in which A, L and B typeinstructions are handled, is decoupled from the back of the pipeline, inwhich E, and S type instructions are handled. This decoupling occurs atthe point at which the data cache and its backing memory is referenced;similarly, a FIFO that is filled by the instruction fetch unit decouplesinstruction cache references from the front of the pipeline shown above.The depth of the FIFO structures is implementation-dependent, i.e. notfixed by the architecture. FIG. 13 further illustrates this pipelineorganization. Accordingly, the latency of load instructions can behidden, as execute instructions are deferred until the results of theload are available. Nevertheless, the execution unit still processesinstructions in normal order, and provides precise exceptions. Moredetails relating to this pipeline structure is explained in the“Superspring Pipeline” section of the Appendix.

A difficulty in particular pipeline structures is that dependentoperations must be separated by the latency of the pipeline, and forhighly pipelined machines, the latency of simple operations can be quitesignificant. According to one embodiment of the present invention, veryhighly pipelined implementations are provided by alternating executionof two or more independent threads. In an embodiment, a thread is thestate required to maintain an independent execution; the architecturalstate required is that of the register file contents, program counter,privilege level, local TB, and when required, exception status. In anembodiment, ensuring that only one thread may handle an exception at onetime may minimize the latter state, exception status. In order to ensurethat all threads make reasonable forward progress, several of themachine resources must be scheduled fairly.

An example of a resource that is critical that it be fairly shared isthe data memory/cache subsystem. In one embodiment, the processor may beable to perform a load operation only on every second cycle, and a storeoperation only on every fourth cycle. The processor schedules thesefixed timing resources fairly by using a round-robin schedule for anumber of threads that is relatively prime to the resource reuse rates.In one embodiment, five simultaneous threads of execution ensure thatresources which may be used every two or four cycles are fairly sharedby allowing the instructions which use those resources to be issued onlyon every second or fourth issue slot for that thread. More detailsrelating to this pipeline structure are explained in the “SuperthreadPipeline” section of the Appendix.

Referring back to FIG. 4, with regard to the sharing of execution units,one embodiment of the present invention employs several differentclassics of functional units for the execution unit, with varying cost,utilization, and performance. In particular, the G units, which performsimple addition and bitwise operations is relatively inexpensive (inarea and power) compared to the other units, and its utilization isrelatively high. Consequently, the design employs four such units, whereeach unit can be shared between two threads. The X unit, which performsa broad class of data switching functions is more expensive and lessused, so two units are provided that are each shared among two threads.The T unit, which performs the Wide Translate instruction, is expensiveand utilization is low, so the single unit is shared among all fourthreads. The E unit, which performs the class of Ensemble instructions,is very expensive in area and power compared to the other functionalunits, but utilization is relatively high, so we provide two such units,each unit shared by two threads.

In FIG. 4, four copies of an access unit are shown, each with an accessinstruction fetch queue A-Queue 401-404, coupled to an access registerfile AR 405-408, each of which is, in turn, coupled to two accessfunctional units A 409-416. The access units function independently forfour simultaneous threads of execution. These eight access functionalunits A 409-416 produce results for access register files AR 405-408 andaddresses to a shared memory system 417. The memory contents fetchedfrom memory system 417 are combined with execute instructions notperformed by the access unit and entered into the four executeinstruction queues E-Queue 421-424. Instructions and memory data fromE-queue 421-424 are presented to execution register files 425-428, whichfetches execution register file source operands. The instructions arecoupled to the execution unit arbitration unit Arbitration 431, thatselects which instructions from the four threads are to be routed to theavailable execution units E 441 and 449, X 442 and 448, G 443-444 and446-447, and T 445. The execution register file source operands ER425-428 are coupled to the execution units 441-445 using source operandbuses 451-454 and to the execution units 445-449 using source operandbuses 455-458. The function unit result operands from execution units441-445 are coupled to the execution register file using result bus 461and the function units result operands from execution units 445-449 arecoupled to the execution register file using result bus 462.

The foregoing elements of the present invention may be better understoodwith reference to the attached Appendix.

In a still further aspect of the present invention, an improvedinterprivilege gateway is described which involves increased parallelismand leads to enhanced performance. In U.S. application Ser. No.08/541,416, now U.S. Pat. No. 6,101,590, a system and method isdescribed for implementing an instruction that, in a controlled fashion,allows the transfer of control (branch) from a lower-privilege level toa higher-privilege level. Embodiment of the present invention providesan improved system and method for a modified instruction thataccomplishes the same purpose but with specific advantages.

Many processor resources, such as control of the virtual memory systemitself, input and output operations, and system control functions areprotected from accidental or malicious misuse by enclosing them in aprotective, privileged region. Entry to this region must be establishedonly though particular entry points, called gateways, to maintain theintegrity of these protected regions.

Prior art versions of this operation generally load an address from aregion of memory using a protected virtual memory attribute that is onlyset for data regions that contain valid gateway entry points, thenperform a branch to an address contained in the contents of memory.Basically, three steps were involved: load, branch, then check. Comparedto other instructions, such as register-to-register computationinstructions and memory loads and stores, and register-based branches,this is a substantially longer operation, which introduces delays andcomplexity to a pipelined implementation.

In the present invention, the branch-gateway instruction performs twooperations in parallel: 1) a branch is performed to the contents ofregister 0 and 2) a load is performed using the contents of register 1,using a specified byte order (little-endian) and a specified size (64bits). If the value loaded from memory does not equal the contents ofregister 0, the instruction is aborted due to an exception. In addition,3) a return address (the next sequential instruction address followingthe branch-gateway instruction) is written into register 0, provided theinstruction is not aborted. This approach essentially uses a firstinstruction to establish the requisite permission to allow user code toaccess privileged code, and then a second instruction is permitted tobranch directly to the privileged code because of the permissions issuedfor the first instruction.

In the present invention, the new privilege level is also contained inregister 0, and the second parallel operation does not need to beperformed if the new privilege level is not greater than the oldprivilege level. When this second operation is suppressed, the remainderof the instruction performs an identical function to a branch-linkinstruction, which is used for invoking procedures that do not requirean increase in privilege. The advantage that this feature brings is thatthe branch-gateway instruction can be used to call a procedure that mayor may not require an increase in privilege.

The memory load operation verifies with the virtual memory system thatthe region that is loaded has been tagged as containing valid gatewaydata. A further advantage of the present invention is that the calledprocedure may rely on the fact that register 1 contains the address thatthe gateway data was loaded from, and can use the contents of register 1to locate additional data or addresses that the procedure may require.Prior art versions of this instruction required that an additionaladdress be loaded from the gateway region of memory in order toinitialize that address in a protected manner—the present inventionallows the address itself to be loaded with a “normal” load operationthat does not require special protection.

The present invention allows a “normal” load operation to also load thecontents of register 0 prior to issuing the branch-gateway instruction.The value may be loaded from the same memory address that is loaded bythe branch-gateway instruction, because the present invention contains avirtual memory system in which the region may be enabled for normal loadoperations as well as the special “gateway” load operation performed bythe branch-gateway instruction.

In a further aspect of the present invention, a system and method isprovided for performing a three-input bitwise Boolean operation in asingle instruction. A novel method described in detail in appendix isused to encode the eight possible output states of such an operationinto only seven bits, and decoding these seven bits back into the eightstates.

In yet a further aspect to the present invention, a system and method isdescribed for improving the branch prediction of simple repetitive loopsof code. The method includes providing a count field for indicating howmany times a branch is likely to be taken before it is not taken, whichenhances the ability to properly predict both the initial and finalbranches of simple loops when a compiler can determine the number ofiterations that the loop will be performed. This improves performance byavoiding misprediction of the branch at the end of a loop.

Memory Management

This section discusses the caches, the translation mechanisms, thememory interfaces, and how the multiprocessor interface is used tomaintain cache coherence.

a. Overview

FIG. 14 is a diagram illustrating the basic organization of the memorymanagement system according to one embodiment of the invention. Inaccordance with this embodiment, the processor provides for both localand global virtual addressing, arbitrary page sizes, and coherent-cachemultiprocessing. The memory management system is designed to provide therequirements for implementation of virtual machines as well as virtualmemory. All facilities of the memory management system are themselvesmemory mapped, in order to provide for the manipulation of thesefacilities by high-level language, compiled code. The translationmechanism is designed to allow full byte-at-a-time control of access tothe virtual address space, with the assistance of fast exceptionhandlers. Privilege levels provide for the secure transition betweeninsecure user code and secure system facilities. Instructions execute ata privilege, specified by a two-bit field in the access information.Zero is the least-privileged level, and three is the most-privilegedlevel.

In general terms, the memory management starts from a local virtualaddress. The local virtual address is translated to a global virtualaddress by an LTB (Local Translation Buffer). In turn, the globalvirtual address is translated to a physical address by a GTB (GlobalTranslation Buffer). One of the addresses, a local virtual address, aglobal virtual address, or a physical address, is used to index thecache data and cache tag arrays, and one of the addresses is used tocheck the cache tag array for cache presence. Protection information isassembled from the LTB, GTB, and optionally the cache tag, to determineif the access is legal.

This form varies somewhat, depending on implementation choices made.Because the LTB leaves the lower 48 bits of the address alone, indexingof the cache arrays with the local virtual address is usually identicalto cache arrays indexed by the global virtual address. However, indexingcache arrays by the global virtual address rather than the physicaladdress produces a coherence issue if the mapping from global virtualaddress to physical is many-to-one.

Starting from a local virtual address, the memory management systemperforms three actions in parallel: the low-order bits of the virtualaddress are used to directly access the data in the cache, a low-orderbit field is used to access the cache tag, and the high-order bits ofthe virtual address are translated from a local address space to aglobal virtual address space.

Following these three actions, operations vary depending upon the cacheimplementation. The cache tag may contain either a physical address andaccess control information (a physically-tagged cache), or may contain aglobal virtual address and global protection information (avirtually-tagged cache).

For a physically-tagged cache, the global virtual address is translatedto a physical address by the GTB, which generates global protectioninformation. The cache tag is checked against the physical address, todetermine a cache hit. In parallel, the local and global protectioninformation is checked.

For a virtually-tagged cache, the cache tag is checked against theglobal virtual address, to determine a cache hit, and the local andglobal protection information is checked. If the cache misses, theglobal virtual address is translated to a physical address by the GTB,which also generates the global protection information.

b. Local Translation Buffer

The 64-bit global virtual address space is global among all tasks. In amultitask environment, requirements for a task-local address space arisefrom operations such as the UNIX “fork” function, in which a task isduplicated into parent and child tasks, each now having a unique virtualaddress space. In addition, when switching tasks, access to one task'saddress space must be disabled and another task's access enabled.

The processor provides for portions of the address space to be madelocal to individual tasks, with a translation to the global virtualspace specified by four 16-bit registers for each local virtual space.The registers specify a mask selecting which of the high-order 16address bits are checked to match a particular value, and if they match,a value with which to modify the virtual address. The processor avoidssetting a fixed page size or local address size; these can be set bysoftware conventions.

A local virtual address space is specified by the following:

local virtual address space specifiers field name size description lm 16mask to select fields of local virtual address to perform match over la16 value to perform match with masked local virtual address lx 16 valueto xor with local virtual address if matched lp 16 local protectionfield (detailed later)

There are as many LTB as threads, and up to 23 (8) entries per LTB. Eachentry is 128 bits, with the high order 64 bits reserved. FIG. 15illustrates the physical address of an LTB entry for thread th, entryen, byte b.

FIG. 16 illustrates a definition for AccessPhysicalLTB. FIG. 17illustrates how various 16-bit values are packed together into a 64-bitLTB entry. The LTB contains a separate context of register sets for eachthread, indicated by the th index above. A context consists of one ormore sets of lm/la/lx/lp registers, one set for each simultaneouslyaccessible local virtual address range, indicated by the en index above.This set of registers is called the “Local TB context,” or LTB (LocalTranslation Buffer) context. The effect of this mechanism is to providethe facilities normally attributed to segmentation. However, in thissystem there is no extension of the address range, instead, segments arelocal nicknames for portions of the global virtual address space.

A failure to match an LTB entry results either in an exception or anaccess to the global virtual address space, depending on privilegelevel. A single bit, selected by the privilege level active for theaccess from a four bit control register field, global access, gadetermines the result. If gaPL is zero (0), the failure causes anexception, if it is one (1), the failure causes the address to bedirectly used as a global virtual address without modification.

FIG. 18 illustrates global access as fields of a control register.Usually, global access is a right conferred to highly privilege levels,so a typical system may be configured with ga0 and ga1 clear (0), butga2 and ga3 set (1). A single low-privilege (0) task can be safelypermitted to have global access, as accesses are further limited by therwxg privilege fields. A concrete example of this is an emulation task,which may use global addresses to simulate segmentation, such as an x86emulation. The emulation task then runs as privilege 0, with ga0 set,while most user tasks run as privilege 1, with ga1 clear. Operatingsystem tasks then use privilege 2 and 3 to communicate with and controlthe user tasks, with ga2 and ga3 set.

For tasks that have global access disabled at their current privilegelevel, failure to match an LTB entry causes an exception. The exceptionhandler may load an LTB entry and continue execution, thus providingaccess to an arbitrary number of local virtual address ranges.

When failure to match an LTB entry does not cause an exception,instructions may access any region in the local virtual address space,when an LTB entry matches, and may access regions in the global virtualaddress space when no LTB entry matches. This mechanism permitsprivileged code to make judicious use of local virtual address ranges,which simplifies the manner in which privileged code may manipulate thecontents of a local virtual address range on behalf of a less-privilegedclient. Note, however, that under this model, an LTB miss does not causean exception directly, so the use of more local virtual address rangesthan LTB entries requires more care: the local virtual address rangesshould be selected so as not to overlap with the global virtual addressranges, and GTB misses to LVA regions must be detected and cause thehandler to load an LTB entry.

Each thread has an independent LTB, so that threads may independentlydefine local translation. The size of the LTB for each thread isimplementation dependent and defined as the LE parameter in thearchitecture description register. LE is the log of the number ofentries in the local TB per thread; an implementation may define LE tobe a minimum of 0, meaning one LTB entry per thread, or a maximum of 3,meaning eight LTB entries per thread. For the initial Zeusimplementation, each thread has two entries and LE=1.

A minimum implementation of an LTB context is a single set oflm/la/lx/lp registers per thread. However, the need for the LTB totranslate both code addresses and data addresses imposes some limits onthe use of the LTB in such systems. We need to be able to guaranteeforward progress. With a single LTB set per thread, either the code orthe data must use global addresses, or both must use the same localaddress range, as must the LTB and GTB exception handler. To avoid thisrestriction, the implementation must be raised to two sets per thread,at least one for code and one for data, to guarantee forward progressfor arbitrary use of local addresses in the user code (but still belimited to using global addresses for exception handlers).

As shown in FIG. 19, a single-set LTB context may be further simplifiedby reserving the implementation of the lm and la registers, setting themto a read-only zero value: Note that in such a configuration, only asingle LA region can be implemented.

If the largest possible space is reserved for an address spaceidentifier, the virtual address is partitioned as shown in FIG. 20. Anyof the bits marked as “local” below may be used as “offset” as desired.

To improve performance, an implementation may perform the LTBtranslation on the value of the base register (rc) or unincrementedprogram counter, provided that a check is performed which prohibitschanging the unmasked upper 16 bits by the add or increment. If thisoptimization is provided and the check fails, anAccessDisallowedByVirtualAddress should be signaled. If thisoptimization is provided, the architecture description parameter LB=1.Otherwise LTB translation is performed on the local address, la, nochecking is required, and LB=0.

As shown in FIG. 21, the LTB protect field controls the minimumprivilege level required for each memory action of read (r), write (w),execute (x), and gateway (g), as well as memory and cache attributes ofwrite allocate (wa), detail access (da), strong ordering (so), cachedisable (cd), and write through (wt). These fields are combined withcorresponding bits in the GTB protect field to control these attributesfor the mapped memory region.

The meaning of the fields are given by the following table:

name size meaning g 2 minimum privilege required for gateway access x 2minimum privilege required for execute access w 2 minimum privilegerequired for write access r 2 minimum privilege required for read access0 1 reserved da 1 detail access so 1 strong ordering cc 3 cache control

FIG. 22 illustrates a definition for LocalTranslation.

c. Global Translation Buffer

Global virtual addresses which fail to be accessed in either the LZC,the MTB, the BTB, or PTB are translated to physical references in atable, here named the “Global Translation Buffer,” (GTB).

Each processor may have one or more GTB's, with each GTB shared by oneor more threads. The parameter GT, the base-two log of the number ofthreads which share a GTB, and the parameter T, the number of threads,allow computation of the number of GTBs (T/2GT), and the number ofthreads which share each GTB (2GT).

If there are two GTBs and four threads (GT=1, T=4), GTB 0 servicesreferences from threads 0 and 1, and GTB 1 services references fromthreads 2 and 3. In the first implementation, there is one GTB, sharedby all four threads. (GT=2, =4).The GTB has 128 entries (G=7).

Per clock cycle, each GTB can translate one global virtual address to aphysical address, yielding protection information as a side effect.

A GTB miss causes a software trap. This trap is designed to permit afast handler for GlobalTBMiss to be written in software, by permitting asecond GTB miss to occur as an exception, rather than a machine check.

There may be as many GTB as threads, and up to 215 entries per GTB. FIG.23 illustrates the physical address of a GTB entry for thread th, entryen, byte b. Note that in FIG. 23, the low-order GT bits of the th valueare ignored, reflecting that 2GT threads share a single GTB. A singleGTB shared between threads appears multiple times in the address space.GTB entries are packed together so that entries in a GTB areconsecutive:

FIG. 24 illustrates a definition for AccessPhysicalGTB. FIG. 25illustrates the format of a GTB entry. As shown, each GTB entry is 128bits.gs=ga+size/2: 256≦size≦264, ga, global address, is aligned (amultiple of) size. px=pa^ga. pa, ga, and px are all aligned (a multipleof) size.

The meaning of the fields are given by the following table:

name size meaning gs 57 global address with size px 56 physical xor g 2minimum privilege required for gateway access x 2 minimum privilegerequired for execute access w 2 minimum privilege required for writeaccess r 2 minimum privilege required for read access 0 1 reserved da 1detail access so 1 strong ordering cc 3 cache control

If the entire contents of the GTB entry is zero (0), the entry will notmatch any global address at all. If a zero value is written, a zerovalue is read for the GTB entry. Software must not write a zero valuefor the gs field unless the entire entry is a zero value.

It is an error to write GTB entries that multiply match any globaladdress; all GTB entries must have unique, non-overlapping coverage ofthe global address space. Hardware may produce a machine check if suchoverlapping coverage is detected, or may produce any physical addressand protection information and continue execution.

Limiting the GTB entry size to 128 bits allows up to replace entriesatomically (with a single store operation), which is less complex thanthe previous design, in which the mask portion was first reduced, thenother entries changed, then the mask is expanded. However, it islimiting the amount of attribute information or physical address rangewe can specify. Consequently, we are encoding the size as a singleadditional bit to the global address in order to allow for attributeinformation. FIG. 26 illustrates a definition forGlobalAddressTranslation.

d. GTB Registers

Because the processor contains multiple threads of execution, even whentaking virtual memory exceptions, it is possible for two threads tonearly simultaneously invoke software GTB miss exception handlers forthe same memory region. In order to avoid producing improper GTB statein such cases, the GTB includes access facilities for indivisiblychecking and then updating the contents of the GTB as a result of amemory write to specific addresses.

A 128-bit write to the address GTBUpdateFill (fill=1), as a side effect,causes first a check of the global address specified in the data againstthe GTB. If the global address check results in a match, the data isdirected to write on the matching entry. If there is no match, theaddress specified by GTBLast is used, and GTBLast is incremented. Ifincrementing GTBLast results in a zero value, GTBLast is reset toGTBFirst, and GTBBump is set. Note that if the size of the updated valueis not equal to the size of the matching entry, the global address checkmay not adequately ensure that no other entries also cover the addressrange of the updated value. The operation is unpredictable if multipleentries match the global address.

The GTBUpdateFill register is a 128-bit memory-mapped location, to whicha write operation performs the operation defined above. A read operationreturns a zero value. The format of the GTBUpdateFill register isidentical to that of a GTB entry.

An alternative write address, GTBUpdate, (fill=0) updates a matchingentry, but makes no change to the GTB if no entry matches. Thisoperation can be used to indivisibly update a GTB entry as to protectionor physical address information. FIG. 27 illustrates a definition forGTBUpdateWrite.

There may be as many GTB as threads, and up to 211 registers per GTB (5registers are implemented). FIG. 28 illustrates the physical address ofa GTB control register for thread th, register rn, byte b. Note that inFIG. 28, the low-order GT bits of the th value are ignored, reflectingthat 2GT threads share single GTB registers. A single set of GTBregisters shared between threads appears multiple times in the addressspace, and manipulates the GTB of the threads with which the registersare associated.

The GTBUpdate register is a 128-bit memory-mapped location, to which awrite operation performs the operation defined above. A read operationreturns a zero value. The format of the GTBUpdateFill register isidentical to that of a GTB entry. FIG. 29 illustrates the registersGTBLast, GTBFirst, and GTBBump. The registers GTBLast, GTBFirst, andGTBBump are memory mapped. As shown in FIG. 29, the GTBLast and GTBFirstregisters are G bits wide, and the GTBBump register is one bit.

FIG. 30 illustrates a definition for AccessPhysicalGTBRegisters.

e. Address Generation

The address units of each of the four threads provide up to two globalvirtual addresses of load, store, or memory instructions, for a total ofeight addresses. LTB units associated with each thread translate thelocal addresses into global addresses. The LZC operates on globaladdresses. MTB, BTB, and PTB units associated with each thread translatethe global addresses into physical addresses and cache addresses. (A PTBunit associated with each thread produces physical addresses and cacheaddresses for program counter references.—this is optional, as bylimiting address generation to two per thread, the MTB can be used forprogram references.) Cache addresses are presented to the LOC asrequired, and physical addresses are checked against cache tags asrequired.

Rounding and Exceptions

In accordance with one embodiment of the invention, rounding isspecified within the instructions explicitly, to avoid explicit stateregisters for a rounding mode. Similarly, the instructions explicitlyspecify how standard exceptions (invalid operation, division by zero,overflow, underflow and inexact) are to be handled.

In this embodiment, when no rounding is explicitly named by theinstruction (default), round to nearest rounding is performed, and allfloating-point exception signals cause the standard-specified defaultresult, rather than a trap. When rounding is explicitly named by theinstruction (N: nearest, Z: zero, F: floor, C: ceiling), the specifiedrounding is performed, and floating-point exception signals other thaninexact cause a floating-point exception trap. When X (exact, orexception) is specified, all floating-point exception signals cause afloating-point exception trap, including inexact. More details regardingrounding and exceptions are described in the “Rounding and Exceptions”section of the Appendix.

Group Boolean

In accordance with one embodiment of the invention, the processorhandles a variety Group Boolean operations. For example, FIG. 31Apresents various Group Boolean instructions. FIGS. 31B and 31Cillustrate an exemplary embodiment of a format and operation codes thatcan be used to perform the Boolean instructions shown in FIG. 31A. Asshown in FIGS. 31B and 31C, in this exemplary embodiment, three valuesare taken from the contents of registers rd, rc and rb. The ih and ilfields specify a function of three bits, producing a single bit result.The specified function is evaluated for each bit position, and theresults are catenated and placed in register rd. Register rd is both asource and destination of this instruction.

The function is specified by eight bits, which give the result for eachpossible value of the three source bits in each bit position:

d 1 1 1 1 0 0 0 0 c 1 1 0 0 1 1 0 0 b 1 0 1 0 1 0 1 0 f(d, c, b) f₇ f₆f₅ f₄ f₃ f₂ f₁ f₀

A function can be modified by rearranging the bits of the immediatevalue. The table below shows how rearrangement of immediate valuef_(7 . . . 0) can reorder the operands d,c,b for the same function.

operation immediate f(d, c, b) f₇ f₆ f₅ f₄ f₃ f₂ f₁ f₀ f(c, d, b) f₇ f₆f₃ f₂ f₅ f₄ f₁ f₀ f(d, b, c) f₇ f₅ f₆ f₄ f₃ f₁ f₂ f₀ f(b, c, d) f₇ f₃ f₅f₁ f₆ f₂ f₄ f₀ f(c, b, d) f₇ f₅ f₃ f₁ f₆ f₄ f₂ f₀ f(b, d, c) f₇ f₃ f₆ f₂f₅ f₁ f₄ f₀

By using such a rearrangement, an operation of the form: b=ƒ(d,c,b) canbe recoded into a legal form: b=ƒ(b,d,c). For example, the function:b=ƒ(d,c,b)=d?c:b cannot be coded, but the equivalent function: d=c?b:dcan be determined by rearranging the code for d=ƒ(d,c,b)=d?c:b, which is11001010, according to the rule for ƒ(d,c,b)→ƒ(c,b,d), to the code11011000.

Encoding—Some special characteristics of this rearrangement is the basisof the manner in which the eight function specification bits arecompressed to seven immediate bits in this instruction. As seen in thetable above, in the general case, a rearrangement of operands fromƒ(d,c,b) to ƒ(d,b,c).(interchanging rc and rb) requires interchangingthe values of f₆ and f₅ and the values of f₂ and f₁.

Among the 256 possible functions which this instruction can perform, onequarter of them (64 functions) are unchanged by this rearrangement.These functions have the property that f₆=f₅ and f₂=f₁. The values of rcand rb can be freely interchanged, and so are sorted into rising orfalling order to indicate the value of f₂. These functions are encodedby the values of f₇, f₆, f₄, f₃, and f₀ in the immediate field and f₂ bywhether rc>rb, thus using 32 immediate values for 64 functions.

Another quarter of the functions have f₆=1 and f₅=0. These functions arerecoded by interchanging rc and rb, f₆ and f₅, f₂ and f₁. They thenshare the same encoding as the quarter of the functions where f₆=0 andf₅=1, and are encoded by the values of f₇, f₄, f₃, f₂, f₁, and f₀ in theimmediate field, thus using 64 immediate values for 128 functions.

The remaining quarter of the functions have f₆=f₅ and f₂≠f₁. The half ofthese in which f₂=1 and f₁=0 are recoded by interchanging rc and rb, f₆and f₅, f₂ and f₁. They then share the same encoding as the eighth ofthe functions where f₂=0 and f₁=1, and are encoded by the values of f₇,f₆, f₄, f₃, and f₀ in the immediate field, thus using 32 immediatevalues for 64 functions.

The function encoding is summarized by the table:

f₇ f₆ f₅ f₄ f₃ f₂ f₁ f₀ trc > trb ih il₅ il₄ il₃ il₂ il₁ il₀ rc rb f₆ f₂ f₂ 0 0 f₆ f₇ f₄ f₃ f₀ trc trb f₆ f₂ ~f₂ 0 0 f₆ f₇ f₄ f₃ f₀ trb trc f₆ 01 0 1 f₆ f₇ f₄ f₃ f₀ trc trb f₆ 1 0 0 1 f₆ f₇ f₄ f₃ f₀ trb trc 0 1 1 f₂f₁ f₇ f₄ f₃ f₀ trc trb 1 0 1 f₁ f₂ f₇ f₄ f₃ f₀ trb trc

The function decoding is summarized by the table:

ih il₅ il₄ il₃ il₂ il₁ il₀ rc > rb f₇ f₆ f₅ f₄ f₃ f₂ f₁ f₀ 0 0 0 il₃ il₄il₄ il₂ il₁ 0 0 il₀ 0 0 1 il₃ il₄ il₄ il₂ il₁ 1 1 il₀ 0 1 il₃ il₄ il₄il₂ il₁ 0 1 il₀ 1 il₃ 0 1 il₂ il₁ il₅ il₄ il₀Group Multiplex

In accordance with one embodiment of the invention, the processorhandles group multiplex operations. FIGS. 31D and 31E illustrate anexemplary embodiment of a format and operation codes that can be used toperform the various Group Multiplex instructions. As shown in FIGS. 31Dand 31E, in this exemplary embodiment, the contents of registers rd, rcand rb are fetched. Each bit of the result is equal to the correspondingbit of rc, if the corresponding bit of rd is set, otherwise it is thecorresponding bit of rb. The result is placed into register ra. Whilethe use of three operand registers and a different result register isdescribed here and elsewhere in the present specification, otherarrangements, such as the use of immediate values, may also beimplemented.

The table marked Redundancies in FIG. 31D illustrates that forparticular values of the register specifiers, the Group Multplexoperation performs operations otherwise available within the GroupBoolean instructions. More specifically, when the result register ra isalso present as a source register in the first, second or third sourceoperand position of the operation, the operation is equivalent to theGroup Boolean instruction with arguments of 0×11001010, 0×11100010, or0×11011000 respectively. When the first source operand is the same asthe second or third source operand, the Group Multiplex operation isequivalent to a bitwise OR or AND operation respectively.

Group Add

In accordance with one embodiment of the invention, the processorhandles a variety of fixed-point, or integer, group operations. Forexample, FIG. 32A presents various examples of Group Add instructionsaccommodating different operand sizes, such as a byte (8 bits), doublet(16 bits), quadlet (32 bits), octlet (64 bits), and hexlet (128 bits).FIGS. 32B and 32C illustrate an exemplary embodiment of a format andoperation codes that can be used to perform the various Group Addinstructions shown in FIG. 32A. As shown in FIGS. 32B and 32C, in thisexemplary embodiment, the contents of registers rc and rb arepartitioned into groups of operands of the size specified and added, andif specified, checked for overflow or limited, yielding a group ofresults, each of which is the size specified. The group of results iscatenated and placed in register rd. While the use of two operandregisters and a different result register is described here andelsewhere in the present specification, other arrangements, such as theuse of immediate values, may also be implemented.

In the present embodiment, for example, if the operand size specified isa byte (8 bits), and each register is 128-bit wide, then the content ofeach register may be partitioned into 16 individual operands, and 16different individual add operations may take place as the result of asingle Group Add instruction. Other instructions involving groups ofoperands may perform group operations in a similar fashion.

Group Subtract

Similarly, FIG. 33A presents various examples of Group Subtractinstructions accommodating different operand sizes. FIGS. 33B and 33Cillustrate an exemplary embodiment of a format and operation codes thatcan be used to perform the various Group Subtract instructions. As shownin FIGS. 33B and 33C, in this exemplary embodiment, the contents ofregisters rc and rb are partitioned into groups of operands of the sizespecified and subtracted, and if specified, checked for overflow orlimited, yielding a group of results, each of which is the sizespecified. The group of results is catenated and placed in register rd.

Group Set

FIG. 33A also presents various examples of Group Set instructionsaccommodating different operand sizes. FIG. 33A also presents additionalpseudo-instructions which are equivalent to other Group Set instructionsaccording to the mapping rules further presented in FIG. 33A. FIGS. 33Band 33C illustrate an exemplary embodiment of a format and operationcodes that can be used to perform the various Group Set instructions. Asshown in FIGS. 33B and 33C, in this exemplary embodiment, the contentsof registers rc and rb are partitioned into groups of operands of thesize specified and the specified comparisons are performed, eachproducing a Boolean result repeated to the size specified, yielding agroup of results, each of which is the size specified. The group ofresults is catenated and placed in register rd. In the presentembodiment, certain comparisons between two identically specifiedregisters, for which the result of such comparisons would be predictableno matter what the contents of the register, are used to encodecomparisons against a zero value.

Combination of Group Set and Boolean Operations

In an embodiment of the invention, conditional operations are providedin the sense that the set on condition operations can be used toconstruct bit masks that can select between alternate vectorexpressions, using the bitwise Boolean operations.

Ensemble Divide/Multiply

Embodiments of the invention provide for other fixed-point groupoperations also. FIG. 34A presents various examples of Ensemble Divideand Ensemble Multiply instructions accommodating different operandsizes. FIGS. 34B and 34C illustrate an exemplary embodiment of a formatand operation codes that can be used to perform the various EnsembleDivide and Ensemble Multiply instructions. As shown in FIGS. 34B and34C, in this exemplary embodiment, the contents of registers rc and rbare partitioned into groups of operands of the size specified anddivided or multiplied, yielding a group of results. The group of resultsis catenated and placed in register rd.

Group Compare

FIG. 35A present various examples of Group Compare instructionsaccommodating different operand sizes. FIGS. 35B and 35C illustrate anexemplary embodiment of a format and operational codes that can be usedto perform the various Group Compare instructions. As shown in FIGS. 35Band 35C, in this exemplary embodiment, these operations performcalculations on partitions of bits in two general register values, andgenerate a fixed-point arithmetic exception if the condition specifiedis met. Two values are taken from the contents of registers rd and rc.The specified condition is calculated on partitions of the operands. Ifthe specified condition is true for any partition, a fixed-pointarithmetic exception is generated.

Ensemble Unary

FIG. 36A present various examples of Ensemble Unary instructionsaccommodating different operand sizes. FIGS. 36B and 36C illustrate anexemplary embodiment of a format and operational codes that can be usedto perform the various Ensemble Unary instructions. As shown in FIGS.36B and 36C, in this exemplary embodiment, these operations takeoperands from a register, perform operations on partitions of bits inthe operand, and place the concatenated results in a second register.Values are taken from the contents of register rc. The specifiedoperation is performed, and the result is placed in register rd. Thecode E.SUM.U.1 in FIG. 36A is preferably encoded as E.SUM.U.128.

Ensemble Floating-Point Add, Divide, Multiply, and Subtract

In accordance with one embodiment of the invention, the processor alsohandles a variety floating-point group operations accommodatingdifferent operand sizes. Here, the different operand sizes may representfloating-point operands of different precisions, such as half-precision(16 bits), single-precision (32 bits), double-precision (64 bits), andquad-precision (128 bits). FIG. 37 illustrates exemplary functions thatare defined for use within the detailed instruction definitions in othersections and figures. In the functions set forth in FIG. 37, an internalformat represents infinite-precision floating-point values as afour-element structure consisting of (1) s (sign bit): 0 for positive, 1for negative, (2) t (type): NORM, ZERO, SNAN, QNAN, INFINITY, (3) e(exponent), and (4) f: (fraction). The mathematical interpretation of anormal value places the binary point at the units of the fraction,adjusted by the exponent: (−1)^s*(2^e)*f. The function F converts apacked IEEE floating-point value into internal format. The functionPackF converts an internal format back into IEEE floating-point format,with rounding and exception control.

FIGS. 38A and 39A present various examples of Ensemble Floating PointAdd, Divide, Multiply, and Subtract instructions. FIGS. 38B-C and 39B-Cillustrate an exemplary embodiment of formats and operation codes thatcan be used to perform the various Ensemble Floating Point Add, Divide,Multiply, and Subtract instructions. In these examples, EnsembleFloating Point Add, Divide, and Multiply instructions have been labeledas “EnsembleFloatingPoint.” Also, Ensemble Floating-Point Subtractinstructions have been labeled as “EnsembleReversedFloatingPoint.” Asshown in FIGS. 38B-C and 39B-C, in this exemplary embodiment, thecontents of registers rc and rb are partitioned into groups of operandsof the size specified, and the specified group operation is performed,yielding a group of results. The group of results is catenated andplaced in register rd.

In the present embodiment, the operation is rounded using the specifiedrounding option or using round-to-nearest if not specified. If arounding option is specified, the operation raises a floating-pointexception if a floating-point invalid operation, divide by zero,overflow, or underflow occurs, or when specified, if the result isinexact. If a rounding option is not specified, floating-pointexceptions are not raised, and are handled according to the defaultrules of IEEE 754.

Ensemble Multiply-Add Floating-Point

FIG. 38D present various examples of Ensemble Floating Point MultiplyAdd instructions. FIGS. 38E-F illustrate an exemplary embodiment offormats and operation codes that can be used to perform the variousEnsemble Floating Point Multiply Add instructions. In these examples,Ensemble Floating Point Multiply Add instructions have been labeled as“EnsembleInplaceFloatingPoint.” As shown in FIGS. 38E-F, in thisexemplary embodiment, operations take operands from three registers,perform operations on partitions of bits in the operands, and place theconcatenated results in the third register. Specifically, the contentsof registers rd, rc and rb are partitioned into groups of operands ofthe size specified, and for each partitioned element, the contents ofregisters rc and rb are multiplied and added to the contents of registerrd, yielding a group of results. The group of results is catenated andplaced in register rd. Register rd is both a source and destination ofthis instruction.

In the present embodiment, the operation is rounded using the specifiedrounding option or using round-to-nearest if not specified. If arounding option is specified, the operation raises a floating-pointexception if a floating-point invalid operation, divide by zero,overflow, or underflow occurs, or when specified, if the result isinexact. If a rounding option is not specified, floating-pointexceptions are not raised, and are handled according to the defaultrules of IEEE 754.

Group Scale-Add Floating-Point

FIG. 38G present various examples of Ensemble Floating Point Scale Addinstructions. FIGS. 38H-I illustrate an exemplary embodiment of formatsand operation codes that can be used to perform the various EnsembleFloating Point Scale Add instructions. In these examples, EnsembleFloating Point Scale Add instructions have been labeled as“EnsembleTernaryFloatingPoint.” As shown in FIGS. 38E-F, in thisexemplary embodiment, the contents of registers rd and rc are taken torepresent a group of floating-point operands. Operands from register rdare multiplied with a floating-point operand taken from theleast-significant bits of the contents of register rb and added tooperands from register rc multiplied with a floating-point operand takenfrom the next least-significant bits of the contents of register rb. Theresults are concatenated and placed in register ra. In an exemplaryembodiment, the results are rounded to the nearest representablefloating-point value in a single floating-point operation. In anexemplary embodiment, floating-point exceptions are not raised, and arehandled according to the default rules of IEEE 754. In an exemplaryembodiment, these instructions cannot select a directed rounding mode ortrap on inexact.

Group Set Floating-Point

FIG. 39D also presents various examples of Group Set Floating-pointinstructions accommodating different operand sizes. FIG. 39E alsopresents additional pseudo-instructions which are equivalent to otherGroup Set Floating-Point instructions according to the mapping rulesfurther presented in FIG. 39E. FIGS. 39F and 39G illustrate an exemplaryembodiment of a format and operation codes that can be used to performthe various Group Set instructions. As shown in FIG. 39G, in thisexemplary embodiment, the contents of registers rc and rb arepartitioned into groups of operands of the size specified and thespecified comparisons are performed, each producing a Boolean resultrepeated to the size specified, yielding a group of results, each ofwhich is the size specified. The group of results is catenated andplaced in register rd. If a rounding mode is specified a floating-pointexception is raised if any operand is a SNAN, or when performing a Lessor Greater Equal comparison, any operand is a QNAN. If a rounding optionis not specified, floating-point exceptions are not raised, and arehandled according to the default rules of IEEE 754.

Group Compare Floating-point

FIG. 40A present various examples of Group Compare Floating-pointinstructions accommodating different operand sizes. FIGS. 40B and 40Cillustrate an exemplary embodiment of a format and operational codesthat can be used to perform the various Group Compare Floating-pointinstructions. As shown in FIGS. 40B and 40C, in this exemplaryembodiment, these operations perform calculations on partitions of bitsin two general register values, and generate a floating-point arithmeticexception if the condition specified is met. The contents of registersrd and rc are compared using the specified floating-point condition. Ifthe result of the comparison is true for any corresponding pair ofelements, a floating-point exception is raised. If a rounding option isspecified, the operation raises a floating-point exception if afloating-point invalid operation occurs. If a rounding option is notspecified, floating-point exceptions are not raised, and are handledaccording to the default rules of IEEE 754.

Ensemble Unary Floating-point

FIG. 41A present various examples of Ensemble Unary Floating-pointinstructions accommodating different operand sizes. FIGS. 41B and 41Cillustrate an exemplary embodiment of a format and operational codesthat can be used to perform the various Ensemble Unary Floating-pointinstructions. As shown in FIGS. 41B and 41C, in this exemplaryembodiment, these operations take one value from a register, perform agroup of floating-point arithmetic operations on partitions of bits inthe operands, and place the concatenated results in a register. Thecontents of register rc is used as the operand of the specifiedfloating-point operation. The result is placed in register rd. Theoperation is rounded using the specified rounding option or usinground-to-nearest if not specified. If a rounding option is specified,unless default exception handling is specified, the operation raises afloating-point exception if a floating-point invalid operation, divideby zero, overflow, or underflow occurs, or when specified, if the resultis inexact. If a rounding option is not specified or if defaultexception handling is specified, floating-point exceptions are notraised, and are handled according to the default rules of IEEE 754. Thereciprocal estimate and reciprocal square root estimate instructionscompute an exact result for half precision, and a result with at least12 bits of significant precision for larger formats.

Ensemble Multiply Galois Field

In accordance with one embodiment of the invention, the processorhandles different Galois filed operations. For example, FIG. 42Apresents various examples of Ensemble Multiply Gaois Field instructionsaccommodating different operand sizes. FIGS. 42B and 42C illustrate anexemplary embodiment of a format and operation codes that can be used toperform the Ensemble Multiply Gaois Field instructions shown in FIG.42A. As shown in FIGS. 42B and 32C, in this exemplary embodiment, thecontents of registers rd, rc, and rb are fetched. The specifiedoperation is performed on these operands. The result is placed intoregister ra.

The contents of registers rd and rc are partitioned into groups ofoperands of the size specified and multiplied in the manner ofpolynomials. The group of values is reduced modulo the polynomialspecified by the contents of register rb, yielding a group of results,each of which is the size specified. The group of results is catenatedand placed in register ra.

An ensemble multiply Galois field bytes instruction (E.MULG.8)multiplies operand [d15 d14 d13 d12 d11 d10 d9 d8 d7 d6 d5 d4 d3 d2 d1d0] by operand [c15 c14 c13 c12 c11 c10 c9 c8 c7 c6 c5 c4 c3 c2 c1 c0],modulo polynomial [q], yielding the results [(d15c15 mod q) (d14c14 modq) . . . (d0c0 mod q), as illustrated in FIG. 42D.

Compress, Expand, Rotate and Shift

In one embodiment of the invention, crossbar switch units such as units142 and 148 perform data handling operations, as previously discussed.As shown in FIG. 43A, such data handling operations may include variousexamples of Crossbar Compress, Crossbar Expand, Crossbar Rotate, andCrossbar Shift operations. FIGS. 43B and 43C illustrate an exemplaryembodiment of a format and operation codes that can be used to performthe various Crossbar Compress, Crossbar Expand, Crossbar Rotate, andCrossbar Shift instructions. As shown in FIGS. 43B and 43C, in thisexemplary embodiment, the contents of registers rc and rb are obtainedand the contents of register rc is partitioned into groups of operandsof the size specified and the specified operation is performed using ashift amount obtained from the contents of register rb masked to valuesfrom zero to one less than the size specified, yielding a group ofresults. The group of results is catenated and placed in register rd.

Various Group Compress operations may convert groups of operands fromhigher precision data to lower precision data. An arbitrary half-sizedsub-field of each bit field can be selected to appear in the result. Forexample, FIG. 43D shows an X.COMPRESS.16 rd=rc, 4 operation, whichperforms a selection of bits 19 . . . 4 of each quadlet in a hexlet.Various Group Shift operations may allow shifting of groups of operandsby a specified number of bits, in a specified direction, such as shiftright or shift left. As can be seen in FIG. 43C, certain Group ShiftLeft instructions may also involve clearing (to zero) empty low orderbits associated with the shift, for each operand. Certain Group ShiftRight instructions may involve clearing (to zero) empty high order bitsassociated with the shift, for each operand. Further, certain GroupShift Right instructions may involve filling empty high order bitsassociated with the shift with copies of the sign bit, for each operand.

Shift Merge

In one embodiment of the invention, as shown in FIG. 43E, such datahandling operations may also include various examples of Shift Mergeoperations. FIGS. 43F and 43G illustrate an exemplary embodiment of aformat and operation codes that can be used to perform the various ShiftMerge instructions. As shown in FIGS. 43F and 43G, in this exemplaryembodiment, the contents of registers rd, and rc are obtained and thecontents of register rd and rc are partitioned into groups of operandsof the size specified, and the specified operation is performed using ashift amount obtained from the contents of register rb masked to valuesfrom zero to one less than the size specified, yielding a group ofresults. The group of results is catenated and placed in register rd.Register rd is both a source and destination of this instruction.

Shift Merge operations may allow shifting of groups of operands by aspecified number of bits, in a specified direction, such as shift rightor shift left. As can be seen in FIG. 43G, certain Shift Mergeoperations may involve filling empty bits associated with the shift withcopies of corresponding bits from the contents of register rd, for eachoperand.

Compress, Expand, Rotate and Shift Immediate

In one embodiment of the invention, crossbar switch units such as units142 and 148 perform data handling operations, as previously discussed.As shown in FIG. 43H, such data handling operations may include variousexamples of Crossbar Compress Immediate, Crossbar Expand Immediate,Crossbar Rotate Immediate, and Crossbar Shift Immediate operations.FIGS. 43I and 43J illustrate an exemplary embodiment of a format andoperation codes that can be used to perform the various CrossbarCompress Immediate, Crossbar Expand Immediate, Crossbar RotateImmediate, and Crossbar Shift Immediate instructions. As shown in FIGS.431 and 43J, in this exemplary embodiment, the contents of register rcis obtained and is partitioned into groups of operands of the sizespecified and the specified operation is performed using a shift amountobtained from the instruction masked to values from zero to one lessthan the size specified, yielding a group of results. The group ofresults is catenated and placed in register rd.

Various Group Compress Immediate operations may convert groups ofoperands from higher precision data to lower precision data. Anarbitrary half-sized sub-field of each bit field can be selected toappear in the result. For example, FIG. 43D shows an X.COMPRESS.16rd=rc,4 operation, which performs a selection of bits 19 . . . 4 of eachquadlet in a hexlet. Various Group Shift Immediate operations may allowshifting of groups of operands by a specified number of bits, in aspecified direction, such as shift right or shift left. As can be seenin FIG. 43J, certain Group Shift Left Immediate instructions may alsoinvolve clearing (to zero) empty low order bits associated with theshift, for each operand. Certain Group Shift Right Immediateinstructions may involve clearing (to zero) empty high order bitsassociated with the shift, for each operand. Further, certain GroupShift Right Immediate instructions may involve filling empty high orderbits associated with the shift with copies of the sign bit, for eachoperand.

Shift Merge Immediate

In one embodiment of the invention, as shown in FIG. 43K, such datahandling operations may also include various examples of Shift MergeImmediate operations. FIGS. 43L and 43M illustrate an exemplaryembodiment of a format and operation codes that can be used to performthe various Shift Merge Immediate instructions. As shown in FIGS. 43Land 43M, in this exemplary embodiment, the contents of registers rd andrc are obtained and are partitioned into groups of operands of the sizespecified, and the specified operation is performed using a shift amountobtained from the instruction masked to values from zero to one lessthan the size specified, yielding a group of results. The group ofresults is catenated and placed in register rd. Register rd is both asource and destination of this instruction.

Shift Merge operations may allow shifting of groups of operands by aspecified number of bits, in a specified direction, such as shift rightor shift left. As can be seen in FIG. 43G, certain Shift Mergeoperations may involve filling empty bits associated with the shift withcopies of corresponding bits from the contents of register rd, for eachoperand.

Crossbar Extract

In one embodiment of the invention, data handling operations may alsoinclude a Crossbar Extract instruction. FIGS. 44A and 44B illustrate anexemplary embodiment of a format and operation codes that can be used toperform the Crossbar Extract instruction. As shown in FIGS. 44A and 44B,in this exemplary embodiment, the contents of registers rd, rc, and rbare fetched. The specified operation is performed on these operands. Theresult is placed into register ra.

The Crossbar Extract instruction allows bits to be extracted fromdifferent operands in various ways. Specifically, bits 31 . . . 0 of thecontents of register rb specifies several parameters which control themanner in which data is extracted, and for certain operations, themanner in which the operation is performed. The position of the controlfields allows for the source position to be added to a fixed controlvalue for dynamic computation, and allows for the lower 16 bits of thecontrol field to be set for some of the simpler extract cases by asingle GCOPYI.128 instruction (see the Appendix). The control fields arefurther arranged so that if only the low order 8 bits are non-zero, a128-bit extraction with truncation and no rounding is performed:

The table below describes the meaning of each label:

label bits meaning fsize 8 field size dpos 8 destination position x 1reserved s 1 signed vs. unsigned n 1 reserved m 1 merge vs. extract l 1reserved rnd 2 reserved gssp 9 group size and source position

The 9-bit gssp field encodes both the group size, gsize, and sourceposition, spos, according to the formula gssp=512−4*gsize+spos. Thegroup size, gsize, is a power of two in the range 1 . . . 128. Thesource position, spos, is in the range 0 . . . (2*gsize)−1.

The values in the s, n, m, l, and rnd fields have the following meaning:

values s n m l rnd 0 unsigned extract 1 signed merge 2 3

As shown in FIG. 44C, for the X.EXTRACT instruction, when m=0, theparameters are interpreted to select a fields from the catenatedcontents of registers rd and rc, extracting values which are catenatedand placed in register ra. As shown in FIG. 44D, for acrossbar-merge-extract (X.EXTRACT when m=1), the parameters areinterpreted to merge fields from the contents of register rd with thecontents of register rc. The results are catenated and placed inregister ra.

Ensemble Extract

In one embodiment of the invention, data handling operations may alsoinclude an Ensemble Extract instruction. FIGS. 44E, 44F and 44Gillustrate an exemplary embodiment of a format and operation codes thatcan be used to perform the Ensemble Extract instruction. As shown inFIGS. 44F and 44G, in this exemplary embodiment, the contents ofregisters rd, rc, and rb are fetched. The specified operation isperformed on these operands. The result is placed into register ra.

The Crossbar Extract instruction allows bits to be extracted fromdifferent operands in various ways. Specifically, bits 31 . . . 0 of thecontents of register rb specifies several parameters which control themanner in which data is extracted, and for certain operations, themanner in which the operation is performed. The position of the controlfields allows for the source position to be added to a fixed controlvalue for dynamic computation, and allows for the lower 16 bits of thecontrol field to be set for some of the simpler extract cases by asingle GCOPYI.128 instruction (see the Appendix). The control fields arefurther arranged so that if only the low order 8 bits are non-zero, a128-bit extraction with truncation and no rounding is performed:

The table below describes the meaning of each label:

label bits meaning fsize 8 field size dpos 8 destination position x 1reserved s 1 signed vs. unsigned n 1 complex vs. real multiplication m 1merge vs. extract or mixed-sign vs. same-sign multiplication l 1 limit:saturation vs. truncation rnd 2 rounding gssp 9 group size and sourceposition

The 9-bit gssp field encodes both the group size, gsize, and sourceposition, spos, according to the formula gssp=512−4*gsize+spos. Thegroup size, gsize, is a power of two in the range 1 . . . 128. Thesource position, spos, is in the range 0 . . . (2*gsize)−1.

The values in the s, n, m, l, and rnd fields have the following meaning:

values s n m l rnd 0 unsigned real extract/same-sign truncate F 1 signedcomplex merge/mixed-sign saturate Z 2 N 3 C

As shown in FIG. 44C, for the E.EXTRACT instruction, when m=0, theparameters are interpreted to select a fields from the catenatedcontents of registers rd and rc, extracting values which are catenatedand placed in register ra. As shown in FIG. 44D, for anensemble-merge-extract (E.EXTRACT when m=1), the parameters areinterpreted to merge fields from the contents of register rd with thecontents of register rc. The results are catenated and placed inregister ra. As can be seen from FIG. 44G, the operand portion to theleft of the selected field is treated as signed or unsigned ascontrolled by the s field, and truncated or saturated as controlled bythe t field, while the operand portion to the right of the selectedfield is rounded as controlled by the rnd field.

Deposit and Withdraw

As shown in FIG. 45A, in one embodiment of the invention, data handlingoperations include various Deposit and Withdraw instructions. FIGS. 45Band 45C illustrate an exemplary embodiment of a format and operationcodes that can be used to perform the various Deposit and Withdrawinstructions. As shown in FIGS. 45B and 45C, in this exemplaryembodiment, these operations take operands from a register and twoimmediate values, perform operations on partitions of bits in theoperands, and place the concatenated results in the second register.Specifically, the contents of register rc is fetched, and 7-bitimmediate values are taken from the 2-bit ih and the 6-bit gsfp and gsfsfields. The specified operation is performed on these operands. Theresult is placed into register rd.

FIG. 45D shows legal values for the ih, gsfp and gsfs fields, indicatingthe group size to which they apply. The ih, gsfp and gsfs fields encodethree values: the group size, the field size, and a shift amount. Theshift amount can also be considered to be the source bit field positionfor group-withdraw instructions or the destination bit field positionfor group-deposit instructions. The encoding is designed so thatcombining the gsfp and gsfs fields with a bitwise-and produces a resultwhich can be decoded to the group size, and so the field size and shiftamount can be easily decoded once the group size has been determined.

As shown in FIG. 45E, the crossbar-deposit instructions deposit a bitfield from the lower bits of each group partition of the source to aspecified bit position in the result. The value is either sign-extendedor zero-extended, as specified. As shown in FIG. 45F, thecrossbar-withdraw instructions withdraw a bit field from a specified bitposition in the each group partition of the source and place it in thelower bits in the result. The value is either sign-extended orzero-extended, as specified.

Deposit Merge

As shown in FIG. 45G, in one embodiment of the invention, data handlingoperations include various Deposit Merge instructions. FIGS. 45H and 45Iillustrate an exemplary embodiment of a format and operation codes thatcan be used to perform the various Deposit Merge instructions. As shownin FIGS. 45H and 45I, in this exemplary embodiment, these operationstake operands from two registers and two immediate values, performoperations on partitions of bits in the operands, and place theconcatenated results in the second register. Specifically, the contentsof registers rc and rd are fetched, and 7-bit immediate values are takenfrom the 2-bit ih and the 6-bit gsfp and gsfs fields. The specifiedoperation is performed on these operands. The result is placed intoregister rd.

FIG. 45D shows legal values for the ih, gsfp and gsfs fields, indicatingthe group size to which they apply. The ih, gsfp and gsfs fields encodethree values: the group size, the field size, and a shift amount. Theshift amount can also be considered to be the source bit field positionfor group-withdraw instructions or the destination bit field positionfor group-deposit instructions. The encoding is designed so thatcombining the gsfp and gsfs fields with a bitwise-and produces a resultwhich can be decoded to the group size, and so the field size and shiftamount can be easily decoded once the group size has been determined.

As shown in FIG. 45J, the crossbar-deposit-merge instructions deposit abit field from the lower bits of each group partition of the source to aspecified bit position in the result. The value is merged with thecontents of register rd at bit positions above and below the depositedbit field. No sign- or zero-extension is performed by this instruction.

Shuffle

As shown in FIG. 46A, in one embodiment of the invention, data handlingoperations may also include various Shuffle instructions, which allowthe contents of registers to be partitioned into groups of operands andinterleaved in a variety of ways. FIGS. 46B and 46C illustrate anexemplary embodiment of a format and operation codes that can be used toperform the various Shuffle instructions. As shown in FIGS. 46B and 46C,in this exemplary embodiment, one of two operations is performed,depending on whether the rc and rb fields are equal. Also, FIG. 46B andthe description below illustrate the format of and relationship of therd, rc, rb, op, v, w, h, and size fields.

In the present embodiment, if the rc and rb fields are equal, a 128-bitoperand is taken from the contents of register rc. Items of size v aredivided into w piles and shuffled together, within groups of size bits,according to the value of op. The result is placed in register rd.

FIG. 46C illustrates that for this operation, values of three parametersx, y, and z are computed depending on the value of op, and in eachresult bit position i, a source bit position within the contents ofregister rc is selected, wherein the source bit position is thecatenation of four fields, the first and fourth fields containing fieldsof i which are unchanged: 6 . . . x and y−1 . . . 0, and the second andthird fields containing a subfield of i, bits x−1 . . . y which isrotated by an amount z: y+z−1 . . . y and x−1 . . . y+z.

Further, if the rc and rb fields are not equal, the contents ofregisters rc and rb are catenated into a 256-bit operand. Items of sizev are divided into w piles and shuffled together, according to the valueof op. Depending on the value of h, a sub-field of op, the low 128 bits(h=0), or the high 128 bits (h=1) of the 256-bit shuffled contents areselected as the result. The result is placed in register rd.

FIG. 46C illustrates that for this operation, the value of x is fixed,and values of two parameters y and z are computed depending on the valueof op, and in each result bit position i, a source bit position withinthe contents of register rc is selected, wherein the source bit positionis the catenation of three fields, the first field containing a fieldsof i which is unchanged: y−1 . . . 0, and the second and third fieldscontaining a subfield of i, bits x−1 . . . y which is rotated by anamount z: y+z−1 . . . y and x−1 . . . y+z.

As shown in FIG. 46D, an example of a crossbar 4-way shuffle of byteswithin hexlet instruction (X.SHUFFLE.128 rd=rcb,8,4) may divide the128-bit operand into 16 bytes and partitions the bytes 4 ways (indicatedby varying shade in the diagram below). The 4 partitions are perfectlyshuffled, producing a 128-bit result. As shown in FIG. 46E, an exampleof a crossbar 4-way shuffle of bytes within triclet instruction(X.SHUFFLE.256 rd=rc,rb,8,4,0) may catenate the contents of rc and rb,then divides the 256-bit content into 32 bytes and partitions the bytes4 ways (indicated by varying shade in the diagram below). The low-orderhalves of the 4 partitions are perfectly shuffled, producing a 128-bitresult.

Changing the last immediate value h to 1 (X.SHUFFLE.256 rd=rc,rb,8,4,1)may modify the operation to perform the same function on the high-orderhalves of the 4 partitions. When rc and rb are equal, the table belowshows the value of the op field and associated values for size, v, andw.

op size v w 0 4 1 2 1 8 1 2 2 8 2 2 3 8 1 4 4 16 1 2 5 16 2 2 6 16 4 2 716 1 4 8 16 2 4 9 16 1 8 10 32 1 2 11 32 2 2 12 32 4 2 13 32 8 2 14 32 14 15 32 2 4 16 32 4 4 17 32 1 8 18 32 2 8 19 32 1 16 20 64 1 2 21 64 2 222 64 4 2 23 64 8 2 24 64 16 2 25 64 1 4 26 64 2 4 27 64 4 4 28 64 8 429 64 1 8 30 64 2 8 31 64 4 8 32 64 1 16 33 64 2 16 34 64 1 32 35 128 12 36 128 2 2 37 128 4 2 38 128 8 2 39 128 16 2 40 128 32 2 41 128 1 4 42128 2 4 43 128 4 4 44 128 8 4 45 128 16 4 46 128 1 8 47 128 2 8 48 128 48 49 128 8 8 50 128 1 16 51 128 2 16 52 128 4 16 53 128 1 32 54 128 2 3255 128 1 64

When rc and rb are not equal, the table below shows the value of theop_(4 . . . 0) field and associated values for size, v, and w: Op₅ isthe value of h, which controls whether the low-order or high-order halfof each partition is shuffled into the result.

op4 . . . 0 size v w 0 256 1 2 1 256 2 2 2 256 4 2 3 256 8 2 4 256 16 25 256 32 2 6 256 64 2 7 256 1 4 8 256 2 4 9 256 4 4 10 256 8 4 11 256 164 12 256 32 4 13 256 1 8 14 256 2 8 15 256 4 8 16 256 8 8 17 256 16 8 18256 1 16 19 256 2 16 20 256 4 16 21 256 8 16 22 256 1 32 23 256 2 32 24256 4 32 25 256 1 64 26 256 2 64 27 256 1 128Swizzle

In one embodiment of the invention, data handling operations may alsoinclude various Crossbar Swizzle instruction. FIGS. 47A and 47Billustrate an exemplary embodiment of a format and operation codes thatcan be used to perform Crossbar Swizzle intructions. As shown in FIGS.47A and 47B, in this exemplary embodiment, the contents of register rcare fetched, and 7-bit immediate values, icopy and iswap, areconstructed from the 2-bit ih field and from the 6-bit icopya and iswapafields. The specified operation is performed on these operands. Theresult is placed into register rd.

The “swizzle” operation can reverse the order of the bit fields in ahexlet. For example, a X.SWIZZLE rd=rc,127,112 operation reverses thedoublets within a hexlet, as shown in FIG. 47C. In some cases, it isdesirable to use a group instruction in which one or more operands is asingle value, not an array. The “swizzle” operation can also copyoperands to multiple locations within a hexlet. For example, a X.SWIZZLE15,0 operation copies the low-order 16 bits to each double within ahexlet.

Select

In one embodiment of the invention, data handling operations may alsoinclude various Crossbar Select instruction. FIGS. 47D and 47Eillustrate an exemplary embodiment of a format and operation codes thatcan be used to perform Crossbar Select instructions. As shown in FIGS.47D and 47E, in this exemplary embodiment, the contents of registers rd,rc and rb are fetched, and the contents of registers rd and rc arecatenated, producing catenated data dc. The contents of register rb ispartitioned into elements, and the value expressed in each partition isemployed to select one partitioned element of the catenated data dc. Theselected elements are catenated together, and result is placed intoregister ra.

Bus Interface

According to one embodiment of the invention, an initial implementationof the processor uses a “Super Socket 7 compatible” (SS7) bus interface,which is generally similar to and compatible with other “Socket 7” and“Super Socket 7” processors. FIG. 48 is a pin summary describing thefunctions of various pins in accordance with the present embodiment.FIGS. 49A-G contain electrical specifications describing AC and DCparameters in accordance with the present embodiment. Further detailsare provided in the “Bus Interface” section of the Appendix.

Load and Load Immediate

As shown in FIGS. 50A and 51A, in one embodiment of the invention,memory access operations may also include various Load and LoadImmediate instructions. These figures and FIGS. 50B and 51B show thatthe various Load and Load Immediate instructions specify a type ofoperand, either signed, or unsigned, represented by omitting orincluding a U, respectively. The instructions further specify a size ofmemory operand, byte, double, quadlet, octlet, or hexlet, representing8, 16, 32, 64, and 128 bits respectively. The instructions furtherspecify aligned memory operands, or not, represented by including a A,or with the A omitted, respectively. The instructions further specify abyte-ordering of the memory operand, either big-endian, orlittle-endian, represented by B, and L respectively.

Each instruction specifies the above items with the followingexceptions: L.8, L.U8, L1.8, L.I.U8 need not distinguish betweenlittle-endian and big-endian ordering, nor between aligned andunaligned, as only a single byte is loaded. L.128.B, L.128.AB, L.128.L,L.128AL, LI.128.B, LI.128.AB, LI.128.L, and LI.128AL need notdistinguish between signed and unsigned, as the hexlet fills thedestination register.

FIGS. 50B and 50C illustrate an exemplary embodiment of formats andoperation codes that can be used to perform Load instructions. As shownin FIGS. 50B and 50C, in this exemplary embodiment, an operand size,expressed in bytes, is specified by the instruction. A virtual addressis computed from the sum of the contents of register rc and thesign-extended value of the offset field, multiplied by the operand size.

FIGS. 51B and 51C illustrate an exemplary embodiment of formats andoperation codes that can be used to perform Load Immediate instructions.As shown in FIGS. 51B and 51C, in this exemplary embodiment, an operandsize, expressed in bytes, is specified by the instruction. A virtualaddress is computed from the sum of the contents of register rc and thesign-extended value of the offset field, multiplied by the operand size.

In an exemplary embodiment, for both Load and Load Immediateinstructions, the contents of memory using the specified byte order areread, treated as the size specified, zero-extended or sign-extended asspecified, and placed into register rd. If alignment is specified, thecomputed virtual address must be aligned, that is, it must be an exactmultiple of the size expressed in bytes. If the address is not alignedan “access disallowed by virtual address” exception occurs.

Store and Store Immediate

As shown in FIGS. 52A and 53A, in one embodiment of the invention,memory access operations may also include various Store and StoreImmediate instructions. These figures and FIGS. 52B and 53B show thatthe various Store and Store Immediate instructions specify a size ofmemory operand, byte, double, quadlet, octlet, or hexlet, representing8, 16, 32, 64, and 128 bits respectively. The instructions furtherspecify aligned memory operands, or not, represented by including a A,or with the A omitted, respectively. The instructions further specify abyte-ordering of the memory operand, either big-endian, orlittle-endian, represented by B, and L respectively.

Each instruction specifies the above items with the followingexceptions: L.8 and LI.8 need not distinguish between little-endian andbig-endian ordering, nor between aligned and unaligned, as only a singlebyte is stored.

FIGS. 52B and 52C illustrate an exemplary embodiment of formats andoperation codes that can be used to perform Store instructions. As shownin FIGS. 52B and 52C, in this exemplary embodiment, an operand size,expressed in bytes, is specified by the instruction. A virtual addressis computed from the sum of the contents of register rc and the contentsof register rb multiplied by operand size.

FIGS. 53B and 53C illustrate an exemplary embodiment of formats andoperation codes that can be used to perform Store Immediateinstructions. As shown in FIGS. 53B and 53C, in this exemplaryembodiment, an operand size, expressed in bytes, is specified by theinstruction. A virtual address is computed from the sum of the contentsof register rc and the sign-extended value of the offset field,multiplied by the operand size.

In an exemplary embodiment, for both Store and Store Immediateinstructions, the contents of register rd, treated as the sizespecified, is stored in memory using the specified byte order. Ifalignment is specified, the computed virtual address must be aligned,that is, it must be an exact multiple of the size expressed in bytes. Ifthe address is not aligned an “access disallowed by virtual address”exception occurs.

Store Multiplex and Store Multiplex Immediate

As shown in FIGS. 52A and 53A, in one embodiment of the invention,memory access operations may also include various Store Multiplex andStore Multiplex Immediate instructions. These figures and FIGS. 52B and53B show that the various Store Multiplex and Store Multiplex Immediateinstructions specify a size of memory operand, octlet, representing 64bits. The instructions further specify aligned memory operands,represented by including a A. The instructions further specify abyte-ordering of the memory operand, either big-endian, orlittle-endian, represented by B, and L respectively.

FIGS. 52B and 52C illustrate an exemplary embodiment of formats andoperation codes that can be used to perform Store Multiplexinstructions. As shown in FIGS. 52B and 52C, in this exemplaryembodiment, an operand size, expressed in bytes, is specified by theinstruction. A virtual address is computed from the sum of the contentsof register rc and the contents of register rb multiplied by operandsize.

FIGS. 53B and 53C illustrate an exemplary embodiment of formats andoperation codes that can be used to perform Store Multiplex Immediateinstructions. As shown in FIGS. 53B and 53C, in this exemplaryembodiment, an operand size, expressed in bytes, is specified by theinstruction. A virtual address is computed from the sum of the contentsof register rc and the sign-extended value of the offset field,multiplied by the operand size.

In an exemplary embodiment, for both Store Multiplex and Store MultiplexImmediate instructions, data contents and mask contents of the contentsof register rd are identified. The data contents are stored in memoryusing the specified byte order for values in which the correspondingmask contents are set. In an exemplary embodiment, it can be understoodthat masked writing of data can be accomplished by indivisibly readingthe original contents of the addressed memory operand, modifying thevalue, and writing the modified value back to the addressed memoryoperand. In an exemplary embodiment, the modification of the value isaccomplished using an operation previously identified as a Multiplexoperation in the section titled Group Multiplex, above, and in FIG. 31E.

In an exemplary embodiment, for both Store Multiplex and Store MultiplexImmediate instructions, the computed virtual address must be aligned,that is, it must be an exact multiple of the size expressed in bytes. Ifthe address is not aligned an “access disallowed by virtual address”exception occurs.

Additional Load and Execute Resources

In an exemplary embodiment, studies of the dynamic distribution ofinstructions on various benchmark suites indicate that the mostfrequently-issued instruction classes are load instructions and executeinstructions. In an exemplary embodiment, it is advantageous to considerexecution pipelines in which the ability to target the machine resourcestoward issuing load and execute instructions is increased.

In an exemplary embodiment, one of the means to increase the ability toissue execute-class instructions is to provide the means to issue twoexecute instructions in a single-issue string. The execution unitactually requires several distinct resources, so by partitioning theseresources, the issue capability can be increased without increasing thenumber of functional units, other than the increased register file readand write ports. In an exemplary embodiment, the partitioning favoredplaces all instructions that involve shifting and shuffling in oneexecution unit, and all instructions that involve multiplication,including fixed-point and floating-point multiply and add in anotherunit. In an exemplary embodiment, resources used for implementing add,subtract, and bitwise logical operations may be duplicated, being modestin size compared to the shift and multiply units. In another exemplaryembodiment, resources used are shared between the two units, as theoperations have low-enough latency that two operations might bepipelined within a single issue cycle. These instructions must generallybe independent, except in another exemplary embodiment that two simpleadd, subtract, or bitwise logical instructions may be performeddependently, if the resources for executing simple instructions areshared between the execution units.

In an exemplary embodiment, one of the means to increase the ability toissue load-class instructions is to provide the means to issue two loadinstructions in a single-issue string. This would generally increase theresources required of the data fetch unit and the data cache, but acompensating solution is to steal the resources for the storeinstruction to execute the second load instruction. Thus, in anexemplary embodiment, a single-issue string can then contain either twoload instructions, or one load instruction and one store instruction,which uses the same register read ports and address computationresources as the basic 5-instruction string in another exemplaryembodiment.

In an exemplary embodiment, this capability also may be employed toprovide support for unaligned load and store instructions, where asingle-issue string may contain as an alternative a single unalignedload or store instruction which uses the resources of the two load-classunits in concert to accomplish the unaligned memory operation.

High-Level Language Accessibility

In one embodiment of the invention, all processor, memory, and interfaceresources directly accessible to high-level language programs. In oneembodiment, memory is byte-addressed, using either little-endian orbig-endian byte ordering. In one embodiment, for consistency with thebit ordering, and for compatibility with x86 processors, little-endianbyte ordering is used when an ordering must be selected. In oneembodiment, load and store instructions are available for bothlittle-endian and big-endian byte ordering. In one embodiment, interfaceresources are accessible as memory-mapped registers. In one embodiment,system state is memory mapped, so that it can be manipulated by compiledcode.

In one embodiment, instructions are specified to assemblers and othercode tools in the syntax of an instruction mnemonic (operation code),then optionally white space followed by a list of operands. In oneembodiment, instruction mnemonics listed in this specification are inupper case (capital) letters, assemblers accept either upper case orlower case letters in the instruction mnemonics. In this specification,instruction mnemonics contain periods (“.”) to separate elements to makethem easier to understand; assemblers ignore periods within instructionmnemonics.

In FIGS. 31B, 31D, 32B, 33B, 34B, 35B, 36B, 38B, 38E, 38H, 39B, 39F,40B, 41B, 42B, 43B, 43F, 43I, 43L, 44A, 44F, 45B, 45H, 46B, 47A, 47D,50B, 51B, 52B, and 53B, the format of instructions to be presented to anassembler is illustrated. Following the assembler format, the format forinclusion of instructions into high-level compiled languages isindicated. Finally, the detailed structure of the instruction fields,including pseudo code used to connect the assembler and compiled formatsto the instruction fields is shown. Further detailed explanation of theformats and instruction decoding is provided in the Appendix, in thesection titled “Instruction Set.”

In one embodiment, an instruction is specifically defined as a four-bytestructure with the little-endian ordering. In one embodiment,instructions must be aligned on four-byte boundaries. In one embodiment,basic floating-point operations supported in hardware are floating-pointadd, subtract, multiply, divide, square root and conversions amongfloating-point formats and between floating-point and binary integerformats. Software libraries provide other operations required by theANSI/IEEE floating-point standard.

In one embodiment, software conventions are employed at software moduleboundaries, in order to permit the combination of separately compiledcode and to provide standard interfaces between application, library andsystem software. In one embodiment, register usage and procedure callconventions may be modified, simplified or optimized when a singlecompilation encloses procedures within a compilation unit so that theprocedures have no external interfaces. For example, internal proceduresmay permit a greater number of register-passed parameters, or haveregisters allocated to avoid the need to save registers at procedureboundaries, or may use a single stack or data pointer allocation tosuffice for more than one level of procedure call.

In one embodiment, at a procedure call boundary, registers are savedeither by the caller or callee procedure, which provides a mechanism forleaf procedures to avoid needing to save registers. Compilers may chooseto allocate variables into caller or callee saved registers depending onhow their lifetimes overlap with procedure calls.

In one embodiment, procedure parameters are normally allocated inregisters, starting from register 2 up to register 9. These registershold up to 8 parameters, which may each be of any size from one byte tosixteen bytes (hexlet), including floating-point and small structureparameters. Additional parameters are passed in memory, allocated on thestack. For C procedures which use varargs.h or stdarg.h and passparameters to further procedures, the compilers must leave room in thestack memory allocation to save registers 2 through 9 into memorycontiguously with the additional stack memory parameters, so thatprocedures such as _doprnt can refer to the parameters as an array.Procedure return values are also allocated in registers, starting fromregister 2 up to register 9. Larger values are passed in memory,allocated on the stack.

In one embodiment, instruction scheduling is performed by a compiler. Inthe manner of software pipelineing, instructions should generally bescheduled so that previous operations can be completed at the time ofissue. When this is not possible, the processor inserts sufficient emptycycles to perform the instructions precisely—explicit no-operationinstructions are not required

CONCLUSION

Having fully described various embodiments of the invention, thoseskilled in the art will recognize, given the teachings herein, thatnumerous alternatives and equivalents exist which do not depart from theinvention. It is therefore intended that the invention not be limited bythe foregoing description, but only by the appended claims.

1. A data processing system comprising: (a) a bus coupling components inthe data processing system; (b) an external memory coupled to the bus;(c) a programmable microprocessor coupled to the bus and capable ofoperation independent of another host processor, the microprocessorcomprising: a data path; an external interface operable to receive datafrom an external source and communicate the received data over the datapath; a cache operable to retain data communicated between the externalinterface and the data path; a register file coupled to the data pathand containing a plurality of registers; and an execution unit coupledto the data path, the execution unit configurable to perform a groupinstruction that operates on a plurality of data elements in partitionedfields of a register to produce a catenated result, the execution unitfurther configurable to execute: (i) an aligned instruction operable tocopy first data according to an aligned memory address, the first datahaving a data width, the data width specified as a fixed value by thealigned instruction, the aligned memory address being one of a pluralityof memory addresses regularly spaced at alignment boundaries separatedby the data width; and (ii) an unaligned instruction operable to copysecond data according to an unaligned memory address, the second datahaving the data width, the data width specified as a fixed value by theunaligned instruction, the second data being permitted to cross analignment boundary of the data width, the unaligned memory address beinga memory address that is not constrained to be one of the plurality ofmemory addresses regularly spaced at alignment boundaries separated bythe data width.
 2. The system of claim 1 wherein the aligned instructioncomprises a load instruction operable to copy the first data from memoryat the aligned memory address to a register, and the unalignedinstruction comprises a load instruction operable to copy the seconddata from memory at the unaligned memory address to a register.
 3. Thesystem of claim 1 wherein the aligned instruction comprises a storeinstruction operable to copy the first data from a register to memory atthe aligned memory address, and the unaligned instruction comprises astore instruction operable to copy the second data from a register tomemory at the unaligned memory address.
 4. The system of claim 1 whereinthe group instruction is capable of operating on data having a datawidth of 128 bits.
 5. The system of claim 1 wherein the groupinstruction is a group floating-point instruction.
 6. The system ofclaim 1 wherein the group instruction is a group integer instruction. 7.The system of claim 1 wherein the aligned instruction and the unalignedinstruction are capable of accessing the first data and the second data,each having the data width of 128 bits.
 8. The system of claim 1 whereinthe aligned instruction and the unaligned instruction are capable ofaccessing the first data and the second data, each having the data widthof 64 bits.
 9. The system of claim 1 wherein the plurality of regularlyspaced memory addresses are separated by intervals of 128 bits.
 10. Thesystem of claim 1 wherein the plurality of regularly spaced memoryaddresses are separated by intervals of 64 bits.
 11. The system of claim1 wherein the aligned instruction responds by generating an exception ifthe aligned memory address is not one of a plurality of memory addressesregularly spaced at alignment boundaries separated by the data width.12. The system of claim 1 wherein the execution unit is furtherconfigurable to execute two aligned instructions in parallel usinghardware capable of executing a single unaligned instruction.
 13. Thesystem of claim 1 wherein the aligned instruction corresponds to a firstbinary code and the unaligned instruction corresponds to a second binarycode, the first binary code matching the second binary code in all butone bit position.
 14. A computer-readable storage medium havinginstructions that cause a computer to perform operations, theinstructions comprising: an instruction that operates on a plurality ofdata elements in partitioned fields of at least one register to producea catenated result; an aligned instruction operable to copy first dataaccording to an aligned memory address, the first data having a datawidth, the data width specified as a fixed value by the alignedinstruction, the aligned memory address being one of a plurality ofmemory addresses regularly spaced by the data width; and an unalignedinstruction operable to copy second data according to an unalignedmemory address, the second data having the data width, the data widthspecified as a fixed value by the unaligned instruction, the unalignedmemory address being a memory address that is not constrained to be oneof the plurality of memory addresses regularly spaced by the data width.15. The computer-readable storage medium of claim 14 wherein the alignedinstruction comprises a load instruction operable to copy the first datafrom memory at the aligned memory address to a register, and theunaligned instruction comprises a load instruction operable to copy thesecond data from memory at the unaligned memory address to a register.16. The computer-readable storage medium of claim 14 wherein the alignedinstruction comprises a store instruction operable to copy the firstdata from a register to memory at the aligned memory address, and theunaligned instruction comprises a store instruction operable to copy thesecond data from a register to memory at the unaligned memory address.17. The computer-readable storage medium of claim 14 wherein the groupinstruction is capable of operating on data having a data width of 128bits.
 18. The computer-readable storage medium of claim 14 wherein thegroup instruction is a group floating-point instruction.
 19. Thecomputer-readable storage medium of claim 14 wherein the groupinstruction is a group integer instruction.
 20. The computer-readablestorage medium of claim 14 wherein the aligned instruction and theunaligned instruction are capable of accessing the first data and thesecond data, each having the data width of 128 bits.
 21. Thecomputer-readable storage medium of claim 14 wherein the alignedinstruction and the unaligned instruction are capable of accessing thefirst data and the second data, each having the data width of 64 bits.22. The computer-readable storage medium of claim 14 wherein theplurality of regularly spaced memory addresses are separated byintervals of 128 bits.
 23. The computer-readable storage medium of claim14 wherein the plurality of regularly spaced memory addresses areseparated by intervals of 64 bits.
 24. The computer-readable storagemedium of claim 14 wherein the aligned instruction responds bygenerating an exception if the aligned memory address is not one of aplurality of memory addresses regularly spaced at alignment boundariesseparated by the data width.
 25. The computer-readable storage medium ofclaim 14 wherein two aligned instructions are capable of parallelexecution.
 26. The computer-readable storage medium of claim 14 whereinthe aligned instruction corresponds to a first binary code and theunaligned instruction corresponds to a second binary code, the firstbinary code matching the second binary code in all but one bit position.